Eliminate JavassistUtils.getLock() and ClassLoaderUtils.withLock()

JavassistUtils.getLock() is a remnant from the time of direct xtend use, where we do not have the ability to synchronize on an object.

Now that we are using Java to interact with JavassistUtils, we can use an external synchronized block. Do just that, migrate the users, eliminate getLock().

Once that is done, ClassLoaderUtils' withLock-style methods are no longer used and need to be eliminated.