[llvm] [NFC][TableGen] Use StringRef in X86RecognizableInstr (PR #139648)

[Pengcheng Wang via llvm-commits]

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@@ -440,8 +440,7 @@ void RecognizableInstr::adjustOperandEncoding(OperandEncoding &encoding) {
 void RecognizableInstr::handleOperand(
     bool optional, unsigned &operandIndex, unsigned &physicalOperandIndex,
     unsigned numPhysicalOperands, const unsigned *operandMapping,
-    OperandEncoding (*encodingFromString)(const std::string &,
-                                          uint8_t OpSize)) {
+    OperandEncoding (*encodingFromString)(StringRef, uint8_t OpSize)) {
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wangpc-pp wrote:

Use `using` or `typedef` for this function type?

https://github.com/llvm/llvm-project/pull/139648