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

[Younan Zhang via cfe-commits]

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@@ -28,16 +28,17 @@ namespace PR12884_original {
       typedef int arg;
     };
     struct C {
-      typedef B::X<typename B::arg> x; // precxx17-warning{{missing 'typename' prior to dependent type name B::X; implicit 'typename' is a C++20 extension}}
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zyn0217 wrote:

A drive-by comment: The test `PR12884_original` is still crashing on trunk but it slips through our testing probably because we somehow stop after errors above - if we move the whole namespace to the top, then we'd immediately run into an assert saying `Unable to find instantiation of declaration!`.

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