We were allowing extra immediate arguments, and only bothering to check
if registers were implicit or not.
Also consolidate extra operand checks in verifier, to make this
testable. We had 3 different places checking if you were trying to build
an instruction with more operands than allowed by the definition. We had
an assertion in addOperand, a direct check in the MIRParser to avoid the
assertion, and the machine verifier checks. Remove the assert and parser
check so the verifier can provide a consistent verification experience,
which will also handle instructions modified in place.
c44dca15a4