[ResetMachineFunctionPass] Add visited functions statistics info
Adding a "NumFunctionsVisited" for collecting the visited function number.
It can be used to collect function pass rate in some tests,
the pass rate = (NumberVisited - NumberReset)/NumberVisited.
e.g. it can be used for caculating GlobalISel pass rate in Test-Suite.
Patch by Tianyang Zhu (zhutianyang)
Differential Revision: https://reviews.llvm.org/D59285