[clang] [clang][AST] Add 'IgnoreTemplateParmDepth' to structural equivalence cache (PR #115518)

[Donát Nagy via cfe-commits]

================
@@ -2511,7 +2512,8 @@ bool StructuralEquivalenceContext::Finish() {
     if (!Equivalent) {
       // Note that these two declarations are not equivalent (and we already
       // know about it).
-      NonEquivalentDecls.insert(P);
+      NonEquivalentDecls.insert(
+          std::make_tuple(D1, D2, IgnoreTemplateParmDepth));
----------------
NagyDonat wrote:

```suggestion
      NonEquivalentDecls[IgnoreTemplateParmDepth].insert(P);
```

https://github.com/llvm/llvm-project/pull/115518