Fixes dotnet#72570.

Still need to delete workarounds that make things public in corelib but maybe this diff is large enough already?

We were gradually getting less and less from reflection blocking:

* We stopped blocking things outside corelib (.NET Native blocked all of BCL; we don't).
* We trim reflection metadata and that allows us to have method bodies without metadata.

With this, we should be able to get type definition-level reflection metadata for any MethodTable there is in the system.

This is a ~30 kB size regression for BasicMinimalApis. It is pretty much a wash for Hello World, because all the BCL cruft to handle reflection blocked types costs as much as the benefit of blocking.

…oding.cs

Co-authored-by: Jan Kotas <jkotas@microsoft.com>

…oding.cs

Co-authored-by: Jan Kotas <jkotas@microsoft.com>