Versioning issue with ComInterop and async variants

[jakobbotsch]

We avoid generating calls to async variants of ComInterop functions. However, there is a versioning issue in the following situation:

1. A call to an interface function is prejitted
2. The interface itself gets marked as ComInterop
3. The interface call is run

In that case we end up with a call to the async variant of a ComInterop function. We currently are not able to generate that. There are a few possible fixes:

• Bring back the async thunk
• Generate an async version based on the IL from the IL stub emitted for the non-async variant
• Move these functions to transient IL plan and have an async version generated that way
• Detect the situation and throw away the R2R codegen

Context: #129747

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[jtschuster]

Wouldn't adding [ComImport] be considered a non-version-safe API change that should require recompilation?
https://learn.microsoft.com/en-us/dotnet/core/compatibility/library-change-rules#attributes