[RuntimeAsync] Some issues with preserving value of a nullable struct with mix of ref/value fields across a suspension point.

[VSadov]

I am not completely sure if this is related to Nullable. Nullable could be special if there was boxing, but this is just a local variable losing its value after Yield. No boxing is involved in this case.
Possibly it is a more general issue with liveness/storing/restoring of mixed value/ref fields of a struct, just a repro happened to involve nullable.

== To repro:
In shared-generics.cs uncomment 2 scenarios marked with
// TODO: uncomment to repro https://github.com/dotnet/runtimelab/issues/3043 and run the test.

The test will fail. It looks like we lose the value here:

    public static async2 Task<T> StaticReturnClassType(T value)
    {
// value != null 
        await Task.Yield();
// value == null
        return value;
    }

Also, I think, while modifying the test with Console.WriteLine(value) in various places to see where exactly the value is lost, I think I have seen the scenario to pass, but lost track to what shape the test was and can't make it pass again. There is a thought that we may be dealing with uninitialized data, maybe...

[VSadov]

CC: @jakobbotsch

[jakobbotsch]

This looks like a problem around certain implicit byref parameters. I can open a fix after #3042 is merged.