[MC] Reorder TARGETInstrTable to shrink MCInstrDesc::ImplicitOffset (#171199)
Put ImplicitOps[] before OperandInfo[] in the generated
TARGETInstrTable. This means that offsets to entries into the (small)
ImplicitOps table do not need to skip over the (large) OperandInfo
table.
This allows shrinking ImplicitOffset from 32 bits to 16 bits
(effectively reverting #138127) which will allow expanding Opcode
instead without increasing the size of MCInstrDesc.