Add SourceGen + Engine

[Evangelink]

No description provided.

[Youssef1313]

Few notes:

• For MSTest.Engine, we need to keep trimming/AOT warnings enabled as it previously was.

• Also https://github.com/microsoft/testanywhere/blob/807751c35848c8e4ab557c0b39bb2c540e70d96d/eng/Analyzers.props#L12-L13

• I'm not sure about https://github.com/microsoft/testanywhere/blob/807751c35848c8e4ab557c0b39bb2c540e70d96d/Directory.Build.props#L45

[Evangelink]

For MSTest.Engine, we need to keep trimming/AOT warnings enabled as it previously was.

Also microsoft/testanywhere@807751c/eng/Analyzers.props#L12-L13

Fixing

I'm not sure about microsoft/testanywhere@807751c/Directory.Build.props#L45

Not needed but thanks for pointing it out