Fix comparison of Structural Values

Fixes a regression from #78041 as reported in the review.  The original
patch failed to compare the canonical type, which this adds.  A slightly
modified test of the original report is added.

(cherry picked from commit e3ee3762304aa81e4a240500844bfdd003401b36)

clang/lib/AST/TemplateBase.cpp

@@ -450,7 +450,8 @@ bool TemplateArgument::structurallyEquals(const TemplateArgument &Other) const {
            getAsIntegral() == Other.getAsIntegral();
 
   case StructuralValue: {
-    if (getStructuralValueType() != Other.getStructuralValueType())
+    if (getStructuralValueType().getCanonicalType() !=
+        Other.getStructuralValueType().getCanonicalType())
       return false;
 
     llvm::FoldingSetNodeID A, B;

clang/test/SemaTemplate/temp_arg_nontype_cxx20.cpp

@@ -336,3 +336,21 @@ template<int ...Ns> void bar(B b) {
   (b.operator Tbar<Ns>(), ...);
 }
 }
+
+namespace ReportedRegression1 {
+  const char kt[] = "dummy";
+
+  template <class T, const char id[]>
+    class SomeTempl { };
+
+  template <const char id[]>
+    class SomeTempl<int, id> {
+      public:
+        int exit_code() const { return 0; }
+    };
+
+  int use() {
+    SomeTempl<int, kt> dummy;
+    return dummy.exit_code();
+  }
+}