[clang-tidy] fix concat-nest-namespace fix hint remove the macro

Partially fixed [#60035](https://github.com/llvm/llvm-project/issues/60035)
This patch refactor the FixHint for concat-nest-namespace.
1. remove each namespace except the last non-nest namespace.
2. replace the last non-nest namespace with the new name.

It can remain the comment / pragma / macro between namespace and update the close comment.

Reviewed By: PiotrZSL

Differential Revision: https://reviews.llvm.org/D147194