[clang-tidy] Fix "Name is not a simple identifier" assertion in `modernize-loop-convert` check.

[hokein]

Summary

Fix assertion failure: "Name is not a simple identifier".

Decl::GetName assumes the name should be an identifier. When the check
processes the function calling statement with speciail key name like
'it.operator->()', it will trigger the assert in GetName.

Rather than using Decl::GetName, we use getNameAsString which works
with special key names in C++.

[bkramer]

looks good.

clang-tidy/modernize/LoopConvertUtils.cpp

case Stmt::CXXOperatorCallExprClass: {
     break;
   }
 
   case Stmt::CXXMemberCallExprClass: {
     const auto *MemCall = cast<CXXMemberCallExpr>(Init);
     // This check is needed because getMethodDecl can return nullptr if the
     // callee is a member function pointer.
     const auto *MDecl = MemCall->getMethodDecl();
-    if (MDecl && !isa<CXXConversionDecl>(MDecl) && MDecl->getName() == "at" &&
-        MemCall->getNumArgs() == 1) {
+    if (MDecl && !isa<CXXConversionDecl>(MDecl) &&
+        MDecl->getNameAsString() == "at" && MemCall->getNumArgs() == 1) {
       return isIndexInSubscriptExpr(MemCall->getArg(0), IndexVar);
     }
     return false;
   }
 
   default:
     break;
   }

test/clang-tidy/modernize-loop-convert-basic.cpp

void f() {
 
   for (U::iterator It = Uu.begin(), E = Uu.end(); It != E; ++It) {
     printf("s has value %d\n", (*It).X);
   }
   // CHECK-MESSAGES: :[[@LINE-3]]:3: warning: use range-based for loop instead
   // CHECK-FIXES: for (auto & It : Uu)
   // CHECK-FIXES-NEXT: printf("s has value %d\n", It.X);
 
+  for (U::iterator It = Uu.begin(), E = Uu.end(); It != E; ++It) {
+    Val* a = It.operator->();
+  }
+
   U::iterator A;
   for (U::iterator I = Uu.begin(), E = Uu.end(); I != E; ++I)
     int K = A->X + I->X;
   // CHECK-MESSAGES: :[[@LINE-2]]:3: warning: use range-based for loop instead
   // CHECK-FIXES: for (auto & I : Uu)
   // CHECK-FIXES-NEXT: int K = A->X + I.X;
 
   dependent<int> V;