[clang-tools-extra] [clangd] Add AddUsingReplaceAll tweak to replace all qualified refere… (PR #204151)

[Dimitri Ratz via cfe-commits]

ratzdi wrote:

> Hello. `prepare()` should be fast. It is used to determine whether or not a tweak can be applied. Heavy operations should only take place within `apply()`. In current implementation `prepare()` is not fast. E.g. `ReplaceQualifiedWithAlias::prepare()` does full AST traversal (and after that we do this full AST traversal again in `apply()`).

Hallo, I try to refactor that issue.

https://github.com/llvm/llvm-project/pull/204151