Runtime async integration and testing

[danroth27]

Tracking issue for any reactionary work needed in ASP.NET Core for the new runtime async support, including testing and investigations to remove existing async performance workarounds.

[agocke]

The main thing that we would need for runtime-async in ASP.NET is the ability to compile differently for different RID targets. In particular, the wasm+mobile RIDs won't fully support runtime-async for NET 11, but the other ones will.

So I could use some advice from ASP.NET infra on how they want to do this. Or I could let copilot handle it :)

[wtgodbe]

I'm the right point of contact for the asp.net infra stuff - I'll need some context on the feature/ask though, maybe we could sync offline about this some time this week

[wtgodbe]

Doing this in #66200

[Youssef1313]

@wtgodbe As your PR got merged, is there anything remaining here?

[wtgodbe]

I don't think so