[clang] [Clang][NFC] Introduce a node to model concept and variable template template parameters (PR #216729)

[Yanzuo Liu via cfe-commits]

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@@ -3488,6 +3460,98 @@ class UnresolvedLookupExpr final
   }
 };
 
+/// A template-id naming a variable template or a concept through a template
+/// template parameter.
+class DependentTemplateIdExpr final
+    : public Expr,
+      private llvm::TrailingObjects<DependentTemplateIdExpr,
+                                    TemplateArgumentLoc> {
+  friend class ASTStmtReader;
+  friend class ASTStmtWriter;
+  friend TrailingObjects;
+
+  NestedNameSpecifierLoc QualifierLoc;
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zwuis wrote:

Can it be nonnull since this AST node refers to a template parameter?

https://github.com/llvm/llvm-project/pull/216729