Bug ID: JDK-8302745 sp > unextended_sp for interpreted to interpreted calls going through method handle linker

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While discussing https://bugs.openjdk.org/browse/JDK-8302320 it was revealed that frame::sp can be greater than frame::unextended_sp when stack walking, in the case where interpreted -> interpreted calls go through a method handle linker method (such as linkToStatic, linkToVirtual, etc.)

These linkers modify the stack by popping the last argument to a call, which is the MemberName appendix argument which points to the actual callee.

However, the linker code doesn't modify the saved sp which the caller writes into r13 (on x64) before making the call. The callee picks up this value, and it later becomes the sender frame's unextended_sp while stack walking. The regular frame::sp is computed as an offset from the base pointer of the callee frame, so we end with a situation where `sp > unextended_sp`.

This violates an invariant in frame::safe_for_sender (and perhaps other places) that `unextended_sp >= sp`.