[clang] [clang-tools-extra] [clang] Improve nested name specifier AST representation (PR #147835)

[Andrey Ali Khan Bolshakov via cfe-commits]

bolshakov-a wrote:

Out of curiosity. The old `getDecl()` methods returned the tag type definition (if present), whereas the new `getOriginalDecl()` returns just some of redeclarations (and not necessarily the first one). What is the reason of such change?

https://github.com/llvm/llvm-project/pull/147835