Custom Marshalers in custom-ALC-loaded assemblies results in types loaded from crossi...

Custom Marshalers in custom-ALC-loaded assemblies results in types loaded from crossing ALCs (#21606)

* Create repro for dotnet/coreclr#19654

* Update ICustomMarshaler.csproj

* Update ICustomMarshaler.csproj

* Clean up repro per feedback.

* Add test case for different assemblies with the same CustomMarshaler name.

* Move EEMarshalingData cache from AppDomain to LoaderAllocator. This fixes the custom-marshaler conflict when using unloadable assembly contexts.

* Internalize the LoaderHeap* parameter.

* Add the pointer to the requesting assembly to the hashtable key.

* Fix linux-musl build break.

* Move Crst out of FEATURE_COMINTEROP block.

* Make sure to copy over the assembly pointer to the key that's actually stored in the hash table.

* Add comment for m_invokingAssembly.

* Move all usages of EEMarshallingData to hang off the correct loader allocator instead of always the global one.

* Change to m_InteropDataCrst since this EEMarshallingData can be used in preemptive GC mode.

* Always init m_InteropDataCrst (since it's used by EEMarshallingData as well as COM).

* PR Feedback.

* Remove extraneous inlines.