[Local GC] Move Weak Reference finalization out of the GC (dotnet/coreclr#10676)

[Local GC] Move Weak Reference finalization out of the GC (dotnet/coreclr#10676)

* [Local GC] Move Weak Reference finalization out of the GC

* Address two issues:
  1) Use GetGCSafeMethodTable instead of GetMethodTable, so that the
     mark bit is correctly masked off the object's method table pointer,
  2) Address code review feedback by re-inserting a missed call to
     GetCanonicalMethodTable and rename the new API to EagerFinalized to
     better illustrate its broader purpose.

* Repair the GC sample

Commit migrated from https://github.com/dotnet/coreclr/commit/be8504bd8a63962c84567990f0b84019f299166c