Parse zero or more assembler input operands, separated by commas.
(parse-?-asm-input-operands parstate) → (mv erp inputs span new-parstate)
If the next token is an open square bracket or a string literal, there must be at least one assembler input operand, so we call the function that parses one or more assembler input operands. If the next token is not an open square bracket or a string literal, then there are no assembler input operands; we return an irrelevant span in this case, which callers do not use.