[clang-rename] Respect the traversal scope when traversing the entire AST.

Summary:
This should be NFC to clang-rename, by default the traversal scope is
TUDecl. Traversing the TUDecl in clangd is a performance cliff, we should
avoid it.

Reviewers: ilya-biryukov

Subscribers: kadircet, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D69892