[release/10.0] [RuntimeAsync] A few fixes for issues found when enabling rt async in Libraries.

[github-actions]

Backport of #119864 to release/10.0

/cc @VSadov

Customer Impact

• Customer reported

• Found internally

• In async methods the GS cookie check, if also present, could end up using (and corrupting) the same register as used to return continuation.

• Synthetic async thunks that provide interop between ordinary task-returning methods and runtime async methods, did not special-case ValueTask, which is sufficiently different to require slightly different IL.

• When multiple awaits are in the same try block, the async analysis could pay attention only to the first one and skip over others.

These bugs require fairly trivial fixes, but otherwise could result in crashes in affected scenarios.

Regression

• Yes
• No

This is new code/scenarios with runtime async.

Testing

The fix was verified on existing libraries tests that caught the issues.

Risk

Low, most changes are to the new code that is only enabled with runtime async.

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.

[dotnet-policy-service]

Tagging subscribers to this area: @mangod9
See info in area-owners.md if you want to be subscribed.

[VSadov]

@AndyAyersMS - could you take a look at this backport PR?

[JulieLeeMSFT]

LGTM. Fixing crash.

[kg]

I don't see anything fatal, so seems fine.

[AndyAyersMS]

JIT changes LGTM.

[JulieLeeMSFT]

Adding @davidwrighton for VM review.

[VSadov]

Thanks!!!

[davidwrighton]

LGTM