[PGO] Add a unit test for the PGOInstrumentationGen pass (#93636)

The patch introduces the gmock-based unittest infrastructure for PGO
Instrumentation and adds some test cases to check whether the
instrumentation has taken place. The testing infrastructure for analysis
modules was borrowed from the LoopPassManagerTest unittest and
simplified a bit to handle module analysis passes only. Actually, we are
testing whether the result of a trivial analysis pass was invalidated by
the PGOInstrumentGen one: we exploit the fact the pass invalidates all
the analysis results after a module was instrumented.

NFC.