[clangd] Fix clang tidy provider when multiple config files exist in directory tree

Currently Clang tidy provider searches from the root directory up to the target directory, this is the opposite of how clang-tidy searches for config files.
The result of this is .clang-tidy files are ignored in any subdirectory of a directory containing a .clang-tidy file.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D96204

(cherry picked from commit ba3ea9c6)