JIT: build pred lists before instrumentation (#81288)

JIT: build pred lists before instrumentation (#81288)

Move pred list building to just before instrumentation (and just after
importation -- we are getting very close to the front of the phase list now).

The block and edge count instrumenters were both using cheap preds to keep
track of some relocated count probes. Revise this so they can use the regular
pred lists. Also rework both approaches so their `RelocateProbes` methods are
fairly similar and perhaps could be unified one day.

Contributes to #80193.