[llvm] [ARM][TableGen][MC] Change the ARM mnemonic operands to be optional for ASM parsing (PR #83436)

[via llvm-commits]

================
@@ -947,8 +947,6 @@ class AsmOperandClass {
   /// instruction if it hasn't matched all the operands yet.  However, this
   /// error will be suppressed if all of the remaining unmatched operands are
   /// marked as IsOptional.
-  ///
-  /// Optional arguments must be at the end of the operand list.
----------------
woruyu wrote:

Thanks Bro, thanks for the case, I have understand that it rely on NumDefaults(from OptionalOperandsMask) to calculate oprerand idx. Thanks again!

https://github.com/llvm/llvm-project/pull/83436