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

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

Is there ANYTHING we can do to split this up?  This is so huge that github is refusing to lead half the changes.

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