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

[Sergei Barannikov via llvm-commits]

================
@@ -3253,7 +3276,7 @@ void AsmMatcherEmitter::run(raw_ostream &OS) {
         const MatchableInfo &A = **I;
         const MatchableInfo &B = **J;
 
-        if (A.couldMatchAmbiguouslyWith(B)) {
+        if (A.couldMatchAmbiguouslyWith(B, Target)) {
----------------
s-barannikov wrote:

```suggestion
        bool PreferSmallerInstructions =
            AsmParser->getValueAsBit("PreferSmallerInstructions");
        if (A.couldMatchAmbiguouslyWith(B, PreferSmallerInstructions)) {
```
Same for shouldBeMatchedBefore above.


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