* Use MessagePackReader \ MessagePackWriter to implement IHubProtocol for server-side Blazor

Fixes #7311

- aspnet/AspNetCore-Internal#1341
- remove Scaffolding references from `build/artifacts.props`, `build/buildorder.props`, `build/submodules.props`, and our templates
- add versions for these packages in `build/dependencies.props` to enable their inclusion in the package archives

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/SignalR/tree/c852bdcc332ffb998ec6a5b226e35d5e74d24009

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

Remove old Submodules

Builds of the packages in aspnet/Extensions repo go through ProdCon instead of building as a submodule of this repo.

This removes EntityFrameworkCore as a git submodule. The EFCore repo will build on its own, and the AspNetCore repo will consume EFCore via PackageReference.