When a deoptimization happens at a MethodHandle call site, we need to restore the preserved SP when we walk the stack.  During the stack walk we don't know yet if the original pc is a MH call site until we built the caller frame, but we only can build the caller frame when we load the correct SP, which depends on whether the call site is a MH call site or not.

To handle this chicken-egg problem we need to introduce a new MH deopt handler so we can easily determine if the deopt happened at a MH call site or not.