Review documentation and test coverage for multimodule assemblies #64367

Multimodule assemblies are not supported in CoreClr. That is a simple statement.

However there are areas, like reflection or emit, where this is observable and we may need to be more detailed regarding the change. There is a possibility that instead of gracefully handling the situation, we may experience crashes or undefined behavior.

We need to review scenarios where multimodule assemblies could get involved in .net FX and.

• document the expectations (most likely some kind of error)
• add regression tests for that
• fix bugs that may be discovered