Currently running a single test only (look for NativeAOT in src\libraries\tests.proj) because in runtimelab we saw some odd race conditions when building multiple test projects. I think I fixed it for .NET 7, but we would need to update the .NET used to build the repo to .NET 7 to pick up the fix and see if the race is gone.

• Make PR validation run at least the System.Runtime, System.Reflection, System.IO.Compression, System.IO.FileSystem, System.Linq.Expressions, System.Threading tests because there are pieces that are meaningfully different for NativeAOT. I might be missing some, but it's a start.
  • We might need to do baselining if any of the tests e.g. depend on Ref.Emit (need to tag them as such so that they don't run), or have single file assumption. Look at System.Reflection as an example: Allow running System.Reflection tests on NativeAOT #67575.
• Add means to run all libraries tests in rolling builds, on all supported platforms.