Don't push handle scope for critical native generic JNI

Leaving a stale handle scope causes problems for the GC the next
time roots are visited. At this point the stack will have other
contents and the GC will attempt to mark many invalid roots.

Bug: 31933313

Test: non preopt eng build booting.
Test: test-art-host

Change-Id: I26607c271a2f50a8a8ab745e8d665e4b3c0778a5