Disable some YieldAwaitable tests on MT.
Add support for constrained calls to Object.Equals to gsharedvt.
Use gsharedvt for some generic instances in full-aot mode to avoid code blowup.
Revert "Use gsharedvt for some generic instances in full-aot mode to avoid code blowup."

This reverts commit 9f36e10b1b87e53335d3dbcea1e570b4d16ea0f4.

Revert this as it breaks some mt tests.
Run YieldAwaitable tests on default synchronization context. Fixes #12446
Enable fixed tests