jni: Switch to @FastNative for all JNI functions.

Switches all (248) methods that previously used !bang JNI in art/libcore
to all use @FastNative.

As a nice benefit, this should be about 1.5x faster than before for those method calls.
This measures out to a 3% startup time improvement for system_server.

Test: make test-art-host
Bug: 34955272
Change-Id: I0881f401c7660c79f275235362777bfa58241deb
33 files changed