jni: Switch to @FastNative for all JNI functions. Deprecate !bang JNI.

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

Also deprecate !bang JNI since nothing in Android seems to (or should
be) using it anymore.

This measures to be a 3% startup time improvement in system_server.

Test: make test-art-host
Bug: 34955272
Change-Id: I0881f401c7660c79f275235362777bfa58241deb
diff --git a/runtime/native/java_lang_VMClassLoader.cc b/runtime/native/java_lang_VMClassLoader.cc
index a8fa7db..54ab861 100644
--- a/runtime/native/java_lang_VMClassLoader.cc
+++ b/runtime/native/java_lang_VMClassLoader.cc
@@ -136,7 +136,7 @@
 }
 
 static JNINativeMethod gMethods[] = {
-  NATIVE_METHOD(VMClassLoader, findLoadedClass, "!(Ljava/lang/ClassLoader;Ljava/lang/String;)Ljava/lang/Class;"),
+  FAST_NATIVE_METHOD(VMClassLoader, findLoadedClass, "(Ljava/lang/ClassLoader;Ljava/lang/String;)Ljava/lang/Class;"),
   NATIVE_METHOD(VMClassLoader, getBootClassPathEntries, "()[Ljava/lang/String;"),
 };