Build primarily with `dotnet msbuild` (#22017)

* Make `dotnet msbuild` the default on Windows too
  - add step using desktop `msbuild` when native builds may be involved
    - `-All` (without `-NoBuildNative`), `-BuildNative` or `-BuildInstallers` run this step
    - but `-ForceCoreMsbuild` unconditionally skips this step

nits:
- add binary log for RepoTasks build if `$BinaryLog` (echoes the `dotnet msbuild` command)
- add blank lines between build steps

* Enable building managed projects depending on native assets
  - splitting native builds out confuses these projects
  - use `$(BuildNative)` less, only to control actual building (not bundling)
  - build both native platforms in one `msbuild` invocation

* Adjust generation scripts to explicitly choose the MSBuild engine
  - ensure native assets are included in GenerateReferenceAssemblies.ps1 build
  - clean up the global state that tools.ps1 corrupts

* Revert move to VS2019.Pre queues

This reverts part of commit b67d161e
- was "[release/5.0-preview5] Update dependencies from dotnet/aspnetcore-tooling (#21710)"

* Revert "!temporary! Require `msbuild` from VS2019 16.6"
  - this reverts commit 58cf2304

* Reduce build duplication in pipelines
  - build native assets and repo tasks once per CI job
  - only cleanup framework references after packing managed projects

nits:
- wrap a few long lines
- remove extra `-forceCoreMsbuild` options in SiteExtensions' build.cmd

* Fix Helix jobs
  - restore.cmd doesn't work well with `-projects`; script unconditionally adds `-all`

* !fixup! Reduce duplications further
  - missed a couple of places `-noBuildRepoTasks` helps

* Cleanup: Remove a few dangling binary logs

* !fixup! Correct typos in generation scripts

* !fixup! Another typo in the generation scripts