[clangd] Change the url for clang-tidy check documentation

In https://github.com/llvm/llvm-project/commit/6e566bc5523f743bc34a7e26f050f1f2b4d699a8, The directory structure of the documentation for clang-tidy checks was changed, however clangd wasn't updated.
Now all the links generated will point to old dead pages.
This updated clangd to use the new page structure.

Reviewed By: sammccall, kadircet

Differential Revision: https://reviews.llvm.org/D128379