TI has a way to patch the native stack to return to *the interpreter* instead of the old code or newly compiled code. So we can put any arbitrary stack frame into the interpreter on demand. This is closer to what jsdbg2's onStep setter actually wants to do than the current singleStepMode, and I suspect the magic we'll be using (Interpoline) will be more heavily tested than the Recompiler.

JM was removed, Baseline implements breakpoints/step mode differently.