[X86] combineCMP - attempt to simplify KSHIFTR mask element extractions when...

[X86] combineCMP - attempt to simplify KSHIFTR mask element extractions when just comparing against zero (REAPPLIED)

We can just bitcast the pre-shifted mask as an integer and use TEST/BT directly.

Reapplied with fix for 239ab16e which didn't set the comparison type correctly