Add pass to strip debug info from MIR

Summary:
Removes:
* All LLVM-IR level debug info using StripDebugInfo()
* All debugify metadata
* 'Debug Info Version' module flag
* All (valid*) DEBUG_VALUE MachineInstrs
* All DebugLocs from MachineInstrs

This is a more complete solution than the previous MIRPrinter
option that just causes it to neglect to print debug-locations.

* The qualifier 'valid' is used here because AArch64 emits
  an invalid one and tests depend on it

Reviewers: vsk, aprantl, bogner

Subscribers: mgorny, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77747