[clang] [AST] Only dump desugared type when visibly different (PR #65214)

[Shafik Yaghmour via cfe-commits]

shafik wrote:

So it looks like some of these changes undo some of the change introduced by @mizvekov in some tests. Maybe @zygoloid or @AaronBallman has some more input here.

https://github.com/llvm/llvm-project/pull/65214