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

[Daniel M. Katz via cfe-commits]

katzdm wrote:

"And on that day, every maintainer of a nontrivial clang fork cried out to the sky in unison."

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