Cleanup and consolidate JVMTI event code.

Various cleanups around JVMTI event code.

Ensure that we always store and restore exceptions.

Ensure we always give agents a local frame.

Ensure that we have static_asserts to verify that we are calling
events with appropriate types.

Various other improvements.

Test: ./test.py --host -j50

Change-Id: I71937d1575efca5096c9d5218203dc8201e3bb79