ART: Add ScopedJitSuspend

Add a helper to suspend the JIT in a scope. This will
wait for the JIT to quiesce, finishing already running
compile jobs. Note that the queue will not be drained,
jobs not picked up by the pool, yet, will remain in
the queue.

Bug: 31385354
Test: m test-art-host
Change-Id: I576e7926423f19a8f382be1263838cd924955f1c