[NativeAOT] Unify implementation of Weak References in all runtimes.

[VSadov]

This mostly covers unification with CoreCLR.
Unification with Mono is nearly done in #76173

A followup to #75436
Since we employ eager finalization, some simplifications are possible. Managed implementation in NativeAOT would be an example.

Ideally CoreClr switches to a managed implementation like in NativeAOT, which seems a lot simpler as it does not need to deal with concerns such as protecting the referenced object and the weak reference instance itself.
The problematic part could be the COM/WINRT/IWeakReference support. Perhaps it can be done via FCall callouts.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[VSadov]

Completed in #77196