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

[Kim Gräsman via cfe-commits]

kimgr wrote:

@sdkrystian It looks like this PR broke IWYU with respect to this assumption:
> Moreover, we don't ever need the type as written -- in almost all cases, we only want the template arguments (e.g. in tooling use-cases).

As I understand it, IWYU did use the type as written to do resugaring of template types, here: https://github.com/include-what-you-use/include-what-you-use/blob/master/iwyu_ast_util.cc#L935

Do you have any tips for how to implement that on top of the new model? Manually type-switch all TemplateArgument kinds and map to a Type, possibly via Expr?

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