[clang] [Clang] Unify interface for accessing template arguments as written for class/variable template specializations (PR #81642)

[Krystian Stasiowski via cfe-commits]

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@@ -2596,23 +2582,24 @@ class VarTemplateSpecializationDecl : public VarDecl,
   llvm::PointerUnion<VarTemplateDecl *, SpecializedPartialSpecialization *>
   SpecializedTemplate;
 
-  /// Further info for explicit template specialization/instantiation.
-  struct ExplicitSpecializationInfo {
-    /// The type-as-written.
-    TypeSourceInfo *TypeAsWritten = nullptr;
+  struct ExplicitInstantiationInfo {
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sdkrystian wrote:

Yeah, I thought about it but I didn't just want to dump it into the clang namespace a la `QualifierInfo`. I'll address this after the test related changes. 

https://github.com/llvm/llvm-project/pull/81642