Entry point clean up.

Create set of entry points needed for image methods to avoid fix-up at load time:
 - interpreter - bridge to interpreter, bridge to compiled code
 - jni - dlsym lookup
 - quick - resolution and bridge to interpreter
 - portable - resolution and bridge to interpreter

Fix JNI work around to use JNI work around argument rewriting code that'd been
accidentally disabled.
Remove abstact method error stub, use interpreter bridge instead.
Consolidate trampoline (previously stub) generation in generic helper.
Simplify trampolines to jump directly into assembly code, keeps stack crawlable.
Dex: replace use of int with ThreadOffset for values that are thread offsets.
Tidy entry point routines between interpreter, jni, quick and portable.

Change-Id: I52a7c2bbb1b7e0ff8a3c3100b774212309d0828e