Replace frame->prev_instr by frame->instr_ptr

[iritkatriel]

frame->prev_instr has confusing semantics, we will replace it by a new field instr_ptr which is

(1) the instruction currently executing (if any), or
(2) the next instruction to execute on the frame (otherwise).

Linked PRs

• gh-109094: replace frame->prev_instr by frame->instr_ptr #109095
• gh-109094: remove unnecessary updates of frame->prev_instr in instrumentation functions #109076
• gh-109094: remove redundant arg to _PyFrame_PushTrampolineUnchecked #110759