[BOLT] Introduce helpers to match `MCInst`s one at a time (NFC)
Introduce matchInst helper function to capture and/or match the operands
of MCInst. Unlike the existing `MCPlusBuilder::MCInstMatcher` machinery,
matchInst is intended for the use cases when precise control over the
instruction order is required. For example, when validating PtrAuth
hardening, all registers are usually considered unsafe after a function
call, even though callee-saved registers should preserve their old
values *under normal operation*.