[MIPatternMatch]: Add mi_match for MachineInstr

This utility allows more efficient start of pattern match.
Often MachineInstr(MI) is available and instead of using
mi_match(MI.getOperand(0).getReg(), MRI, ...) followed by
MRI.getVRegDef(Reg) that gives back MI we now use
mi_match(MI, MRI, ...).

Differential Revision: https://reviews.llvm.org/D99735