[coop] Blacklist two more wrappers when generating safepoints.

[coop] Blacklist two more wrappers when generating safepoints.

A GC Safepoint require the thread to be in GC unsafe mode to run properly.

Both mono_threads_finish_blocking and mono_threads_reset_blocking_start are called
in GC Safe mode, which would cause them to assert in checked-build.

mono_threads_finish_blocking is called after a pinvoke finished, which means the thread will
still be in blocking mode.

mono_threads_reset_blocking_start is called by reverse pinvoke wrappers before calling managed
code, so it will be in blocking mode too.

This looks like something checked-build should catch by setting the polling variable more frequently.