jni: Fast path for @FastNative annotated java methods

Adds a faster path for java methods annotated with
dalvik.annotation.optimization.FastNative .

Intended to replace usage of fast JNI (registering with "!(FOO)BAR" descriptors).

Performance Microbenchmark Results (Angler):
* Regular JNI cost in nanoseconds: 115
* Fast JNI cost in nanoseconds: 60
* @FastNative cost in nanoseconds: 36

Summary: Up to 67% faster (vs fast jni) JNI transition cost

Change-Id: Ic23823ae0f232270c068ec999fd89aa993894b0e