[clang] Fix assertion failure during conversion function overload resolution. (PR #98671)

[Shafik Yaghmour via cfe-commits]

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@@ -1519,7 +1519,8 @@ bool Sema::IsAtLeastAsConstrained(NamedDecl *D1,
     auto IsExpectedEntity = [](const FunctionDecl *FD) {
       FunctionDecl::TemplatedKind Kind = FD->getTemplatedKind();
       return Kind == FunctionDecl::TK_NonTemplate ||
-             Kind == FunctionDecl::TK_FunctionTemplate;
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shafik wrote:

So was `TK_FunctionTemplate` never correct? How do we know we have the right set of expected Entities here?

Do the tests we have cover all three cases here? If not can we add a test that covers all three? If not why can't we?

https://github.com/llvm/llvm-project/pull/98671