Annotate android.os.Debug native heap accessors with @CriticalNative

These methods do not require an Env and don't make any high/variable latency
operations, so should be safe to annotate as such.

Bug: 374158990
Flag: EXEMPT annotation change can't be flagged
Test: presubmit
Change-Id: If62c2ace15d2c60ec518c172990a9c2294eb7395