Switch -Xjnitrace over to using a custom JNI bridge.

This now works without needing to specify -Xint:portable, and no longer needs
to be manually enabled at compile-time.

If you're using -Xjnitrace, you'll pay to look up the real JNI bridge on every
invocation of a native method, but doing so leads to a really simple
implementation, and you're writing to the log on every invocation anyway, so
-Xjnitrace and performance don't go together anyway.

Bug: 2846017

Change-Id: I3108c4f35f27b72e8849c41077ae3e8768550e96
11 files changed