[BOLT] Add option to verify instruction encoder/decoder

Summary:
Add option `-check-encoding` to verify if the input to LLVM disassembler
matches the output of the assembler. When set, the verification runs on
every instruction in processed functions.

I'm not enabling the option by default as it could be quite noisy on x86
where instruction encoding is ambiguous and can include redundant
prefixes.

(cherry picked from FBD16595415)