This addresses the use case in https://github.com/clangd/clangd/issues/1038 where
a user wants to make a .clangd file that is applicable for several subdirectories with
relative paths to the .clangd file (instead of the individual c-files). It does this by
replacing any occurrances of ${CURRENT_FILE_PATH} with the directory of the .clangd file.
The syntax for the text to be replaced is up for discussion.