Clear more native pointers in finalizers

This hopefully handles the remaining finalizers in frameworks/base
that didn't guard against calls from other finalizers after being
finalized.

The goal here is to reduce the possible corruption causes we have
to think about by a few.

If any of theses are either very frequently used, or use large
Java (as opposed to native) objects, we should probably convert them
to NativeAllocationRegistry instead. But that's more work.

Bug: 18178237
Change-Id: I79bc0e8fa20af8f340418a6226022e0294d77f02