[Clang] Fix memory leak due to TemplateArgumentListInfo used in AST node.

It looks like the leak is rooted at the allocation here:
https://github.com/llvm/llvm-project/blob/1a155ee7de3b62a2fabee86fb470a1554fadc54d/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp#L3857

The VarTemplateSpecializationDecl is allocated using placement new which uses the AST structure for ownership: https://github.com/llvm/llvm-project/blob/1a155ee7de3b62a2fabee86fb470a1554fadc54d/clang/lib/AST/DeclBase.cpp#L99

The problem is the TemplateArgumentListInfo inside https://github.com/llvm/llvm-project/blob/1a155ee7de3b62a2fabee86fb470a1554fadc54d/clang/include/clang/AST/DeclTemplate.h#L2721
This object contains a vector which does not use placement new: https://github.com/llvm/llvm-project/blob/1a155ee7de3b62a2fabee86fb470a1554fadc54d/clang/include/clang/AST/TemplateBase.h#L564

Apparently ASTTemplateArgumentListInfo should be used instead https://github.com/llvm/llvm-project/blob/1a155ee7de3b62a2fabee86fb470a1554fadc54d/clang/include/clang/AST/TemplateBase.h#L575

https://reviews.llvm.org/D125802#3551305

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D126944