Add E2E tests that restore the produced packages and compile against public API

https://github.com/dotnet/maintenance-packages/issues/212 showed that we would benefit from E2E tests. I expect the following to be possible:

1. Build the repo as today
2. After the packages got produced, build a set of E2E test projects that restore them and build compile against the public API (typeof might be enough). This could be a static / hardcoded list of test projects or an automated testing process.

The build sequence can be expressed via modifications to the eng/Build.props Arcade build extension point.
The interesting TFMs to target are probably net462, net471, net472, net481, netstandard2.0, netstandard2.1, netcoreapp2.0, net8.0.