[mono] Avoid calling mono_metadata_type_hash () on the container class in mono_generi...

[mono] Avoid calling mono_metadata_type_hash () on the container class in mono_generic_class_hash (). (#71764)

If a class inherits from a generic instance instantiated with itself, then its possible
for mono_generic_class_hash () to be called while the container class is not fully
initialized yet, i.e. byval_arg.type is 0. This would cause the generic class to change
its hash.

Fixes https://github.com/dotnet/runtime/issues/71424.

Co-authored-by: Zoltan Varga <vargaz@gmail.com>