Add complete user parsing/writing support for new stack maps, update emission by classfile and javac. Waiting on VM; current tests only examine class files via the classfile API and updated javap.

Also adopted some later changes, such as if a frame is in post-larval stage, no need for extra larval frame to clear the unsets, rename from assert_unset_fields to early_larval, count changes.

Also removed old classfile library usage, already nuked in mainline; this can ease mainline merge later.