[clang] [clang-tools-extra] [clang] Implement CWG2398 provisional TTP matching to class templates (PR #94981)

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@@ -326,6 +320,48 @@ namespace classes {
       // expected-error at -1 {{no matching function for call}}
     }
   } // namespace packs
+  namespace nested {
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cor3ntin wrote:

Do we need more tests?
Maybe add the example from #100692 ?

https://github.com/llvm/llvm-project/pull/94981