Install the .NET Core SDK into the repo root instead of UserProfile and 'install' copy of AspNetCore shared framework (#7293)

This is required to workaround several limitations in the way the .NET Core SDK finds shared frameworks and targeting packs. It allow tests to use shared frameworks and targeting packs.

It also matches the patterns established in other aspnet and dotnet repos. This should reduce the friction required to adopt Arcade SDK.

## Changes

* This moves the default location of the .NET Core SDK installation into `$repoRoot/.dotnet`. This location was already in use for CI builds. 
* Update the build step for Microsoft.AspNetCore.App to install the shared framework into the local copy of the .NET Core SDK

## Recommendations

* Use the "startvs.cmd" script to launch Visual Studio. This will set required environment variables to make VS happier than if you just double click the .sln file.
* Use "activate.sh/ps1" if you want to run `dotnet build`, `dotnet test` and other dotnet commands. These will set required environment variables, including PATH.
* I recommend removing %USERPROFILE%/.dotnet to your PATH variable if you had added it manually before. This will no longer match what build tools will install.
* `git clean -xfd -e .dotnet/` preserves the folder so you don’t have to re-download the SDK again.

Add new build.cmd/sh options for suppressing restore, NodeJS, setting target arch and OS name, and more (#7137)

Add new command line parameters for working with the project:

* `-NoBuild`, `-NoRestore` - these already existed, but users found it hard to discover this powershell syntax: '-build:$false'
* `-Arch`/`--arch` - set the target CPU architecture to build. Defaults to x64
* `--os-name` - on non-Windows builds, manually specify if the build should target Alpine. generic Linux, or MacOS
* Rename flags used to build specific project types. The pattern now is `--build-$(group)` or `--no-build-$(group)` (In PowerShell its `-Build$(Group)` or `-NoBuild$(Group). Example: -NoBuildJava

Changes to build definitions:
* Update the ci build definition to build all supported architectures
* Support publishing multiple artifacts per job

Other changes:
* `-NoBuild` implies `-NoRestore`
* Add new properties, `TargetArchitecture`, `TargetOsName`, and `TargetRuntimeIdentifier`
* Replace usages of `SharedFxRid` with these new properties
* To make `--no-build-nodejs` actually work, replaced Components.Browser.JS.csproj with Components.Browser.JS.npmproj
* Fix errors when building for win-arm on a clean machine
* Fix a few other project errors, like using the wrong syntax for DefaultItemExcludes, or using the wrong Platform value for x86

Changes:

* Remove obsolete targets which are unnecessary now that this repo no longer builds git submodules in a separate build process
* Remove the need for static analysis of 'ArtifactInfo' items
* Simplify how the code signing task is configured
* Remove unused repo tasks
* Remove duplicate lists of external dependencies and packages to be produced
* Remove obsolete build definition
* Remove obsolete build script parameters
* Add VisualStudioSetupOutputPath

Changes:
* IsProductPackage => IsShippingPackage
* artifacts/$config/packages => artifacts/packages/$config
* packages/product => packages/Shipping
* packages/internal => packages/NonShipping
* Renamed MSBuild properties used for output folders
* Update build tools to use 2 spaces in global.json

Part of #4246 

Changes:
* Update source code layout to follow the new conventions for this repo
* Update project files to use `<Reference>`
* Update targets to build NPM packages
* Update BuildTools to support custom 'restore' and 'test' targets

.NET Core 2.0 reached EOL last year. This removes multi-targeting our test projects and test assets to only use .NET Core 2.1 and .NET Framework 4.6.1.

Fix broken tests and VS solutions caused by source code reorganization and other build infra cleanup

Changes:
* Fix broken tests and VS solutions caused by source code reorganization
* Add a check to validate generated code and solutions on PRs
* backport some source code reorg to src/Identity
* Fix startvs.cmd if you've already run build.ps1
* Add PR checks for tests on Linux/macOS
* Skip broken Nginx tests
* Add conditions to skip IIS tests on non-Windows platforms

Fix VS errors about repotasks when repotasks have not been built, and update documentation to indicate that VS users should invoke restore.cmd first (#6295)

Follow-up to #6078

This should solve race conditions in restoring .wixproj files.

Co-authored-by: Nate McMaster <natemcmaster@users.noreply.github.com>
Co-authored-by: Justin Kotalik <jkotalik@users.noreply.github.com>

This simplifies the way that we publish files to our network drop share.

Changes:
* Instead of explicitly listing every file that needs to publish, use directories to classify packages and artifacts into different categories.
* Add documentation for the expected layout of artifacts/
* Remove the need for static analysis to determine which packages go to which project
* Add the MSBuild property "IsProductPackage" to .csproj files which ship as a package to NuGet.org.

As a result of removing Razor's VS projects and upgrading all projects to netcoreapp3.0, we no longer need dependency variable for .NET Core 1.x and 2.x and Visual Studio packages.

Changes:
* Remove 'StandardTestTfm'
* Remove variables for .NET Core 1.0, 1.1, 2.0, 2.1, and 2.2
* Remove VSIX variables
* Stop generating 'branding.props' - this hasn't been used in a while and is no longer needed

Changes:
* Ensure IIS managed and pkg projects build after the native projects
* Update projects to build test
* Update CI checks to build on macOS and Linux
* Use package baselines to manage ANCM packages

Prior to reorganization, this source code was found in https://github.com/aspnet/Identity/tree/4a717c85635671e04c8691fe3c125a77ee46d32a

Prior to reorganization, this source code was found in https://github.com/aspnet/Identity/tree/4b3d8e5106158fb29da33c8e14134ed168a5e880

Prior to reorganization, this source code was found in https://github.com/aspnet/Identity/tree/fa3cfd08eb6af819adc5fef2d9b603638c4b4b3b

Prior to reorganization, this source code was found in https://github.com/aspnet/Localization/tree/0bcac31dd705fb9db60723f5d7eaeffb728358f5

Prior to reorganization, this source code was found in https://github.com/aspnet/BasicMiddleware/tree/1de636cd18309070792b68888ca29c8b85fac98b

Prior to reorganization, this source code was found in https://github.com/aspnet/Razor/tree/582f3f867eeb8fca00e6b328faf7665c9a98476c

Prior to reorganization, this source code was found in https://github.com/aspnet/MvcPrecompilation/tree/3cd4de8af8322b90e62a5818ece90428e2dc933b

Prior to reorganization, this source code was found in https://github.com/aspnet/Mvc/tree/c9887e027a97b07a3ae7699112b9a2620a36e553

Prior to reorganization, this source code was found in https://github.com/aspnet/SignalR/tree/c852bdcc332ffb998ec6a5b226e35d5e74d24009

Prior to reorganization, this source code was found in https://github.com/aspnet/Razor/tree/8ba0a894256e4b5c5385db9b5aac32fdbd046f3a

Prior to reorganization, this source code was found in https://github.com/aspnet/MvcPrecompilation/tree/032768b063a768559c8dfaea0d06380da77307ae

Prior to reorganization, this source code was found in https://github.com/aspnet/Mvc/tree/a6199bbfbab05583f987bae322fb04566841aaea

Prior to reorganization, this source code was found in https://github.com/aspnet/SignalR/tree/d0bcdf3dd92afba858fca2871535faf4594c81de

Prior to reorganization, this source code was found in https://github.com/aspnet/Razor/tree/fd4572874e41ca3af803b0b2c71955505dd4bde5

Prior to reorganization, this source code was found in https://github.com/aspnet/MvcPrecompilation/tree/617586a984b1eff9ca0ca8126dd0b1dab2ea16f2

Prior to reorganization, this source code was found in https://github.com/aspnet/Mvc/tree/5a4fd3e792e75619e3b1de069fabdf87d2cd0983

Prior to reorganization, this source code was found in https://github.com/aspnet/SignalR/tree/bc148a07244a451e48b7e0efdf16db8f69f788ff

Prior to reorganization, this source code was found in https://github.com/aspnet/Security/tree/26d27d871b7992022c082dc207e3d126e1d9d278

Prior to reorganization, this source code was found in https://github.com/aspnet/Routing/tree/c28c7dea4e866ec5a0d33f0e290bc49baadb1c85

Prior to reorganization, this source code was found in https://github.com/aspnet/ResponseCaching/tree/12395b4d1c03e49134704679f94af6f328a7e1d5