Provide an API to check whether two IL instruction/expression are semantically the same

[xusheng6]

Support we have two IL instructions, e.g., instr1, and instr2, and we wish to know whether they have the same content. instr1 == instr2 does not help, because that will check the two object for equivalence, but the underlying instruction can be the same despite they have a different index.

The API should basically check whether the two instruction has the same operation, and if so, whether each of the operand is equivalent, and do the check recursively on the expression true