[clang-tools-extra] [clang-tidy] Add `readability-redundant-tag` check (PR #210007)

[purnima shrivastava via cfe-commits]

purnima-nlp wrote:

@zwuis I checked the NamedDecl hierarchy and the current [basic.scope.hiding] wording. The declarations that can hide a class or enumeration name are variables, data members, functions, and enumerators. This matches Clang’s existing canHideTag implementation in lib/Sema/SemaLookup.cpp, including FunctionTemplateDecl and UnresolvedUsingValueDecl.

Therefore, I believe the current list is complete for this rule. Could you please confirm whether there is a declaration kind or lookup context I have missed?

https://github.com/llvm/llvm-project/pull/210007