jni: Test that pushed handle scopes are popped after JNI transitions

There was previously a bug in generic JNI for @CriticalNative where new
handle scopes were pushed, but then not popped after the native call
was done. This caused a bug with stale pointers being found by GC.

Bug: 31933313
Change-Id: I423f9e7a7d391ba3a4771c830691931f0025b354