[clang] [Clang][Sema] Use correct TemplateName when transforming TemplateSpecializationType (PR #93411)

[Younan Zhang via cfe-commits]

================
@@ -7216,9 +7216,30 @@ TreeTransform<Derived>::TransformElaboratedType(TypeLocBuilder &TLB,
       return QualType();
   }
 
-  QualType NamedT = getDerived().TransformType(TLB, TL.getNamedTypeLoc());
-  if (NamedT.isNull())
-    return QualType();
+  QualType NamedT;
+  if (SemaRef.getLangOpts().CPlusPlus20 && QualifierLoc &&
+      isa<TemplateSpecializationType>(TL.getNamedTypeLoc().getType())) {
+    TemplateSpecializationTypeLoc SpecTL =
+        TL.getNamedTypeLoc().castAs<TemplateSpecializationTypeLoc>();
+    const TemplateSpecializationType *TST =
+        SpecTL.getType()->castAs<TemplateSpecializationType>();
----------------
zyn0217 wrote:

```c++
if (QualType QT = TL.getNamedTypeLoc().getType(); ... && isa<...>(QT)) {
  auto SpecTL = ...;
  auto *TST = QT.getTypePtr();
}
```

Probably looks better.

https://github.com/llvm/llvm-project/pull/93411