[CodeComplete] Tweak code completion for `typename`.

Summary:
Currently, clangd always completes `typename` as `typename qualifier::name`, I think the current behavior is not useful when the code completion is triggered in `template <>`. So I tweak it to `typename identifier`.

Patch by @lh123 !

Reviewers: sammccall, kadircet

Reviewed By: kadircet

Subscribers: ilya-biryukov, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D82373