Fix ILStubCache allocation for collectible assemblies (dotnet/coreclr#21188)

Fix ILStubCache allocation for collectible assemblies (dotnet/coreclr#21188)

The ILStubCache was being allocated per domain unless the domain was a
compilation AppDomain. This is wrong for collectible assemblies, since
after an assembly is collected, the cache keeps stale entries referring
to already deleted MethodTables.
The fix is to make ILStubChange per LoaderAllocator instead (and keep
the per module instances for compilation AppDomain).

Commit migrated from https://github.com/dotnet/coreclr/commit/8aa0869eb9153429091fdba49469d89ec33092cb