[BOLT] Speedup ICF by better function hashing

Summary:
Too many hash collisions may cause ICF to run slowly.

We used to hash BinaryFunction only looking at instruction opcodes,
ignoring instruction operands. With many almost identical functions,
such approach may lead to long ICF processing time. By including
operands into the hash, we reduce the number of collisions and
improve the runtime often by a factor of 2 or more.

(cherry picked from FBD20888957)