[clang] [clang][NFC] Refactor `Sema::TemplateDeductionResult` (PR #81398)

[Erich Keane via cfe-commits]

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@@ -33,6 +33,7 @@ namespace clang {
 class Decl;
 struct DeducedPack;
 class Sema;
+enum class TemplateDeductionResult;
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erichkeane wrote:

Ok then, I'm ok sticking to our existing practice if this is a policy that was already made.

https://github.com/llvm/llvm-project/pull/81398