[TableGen,GlobalISel] Use MapVector to stabilize iteration order

Otherwise llvm/test/TableGen/GlobalISelCombinerEmitter/type-inference.td
could fail when llvm::hash_value(StringRef) changes.

Fix #66377

Author: MaskRay

llvm/utils/TableGen/GlobalISelCombinerEmitter.cpp

@@ -529,7 +529,7 @@ void CombineRuleOperandTypeChecker::getInstEqClasses(
   const auto MCOITypes = getMCOIOperandTypes(*CGP);
   assert(MCOITypes.size() == P.operands_size());
 
-  DenseMap<StringRef, std::vector<unsigned>> TyToOpIdx;
+  MapVector<StringRef, SmallVector<unsigned, 0>> TyToOpIdx;
   for (const auto &[Idx, Ty] : enumerate(MCOITypes))
     TyToOpIdx[Ty].push_back(Idx);