Problem:
On Windows, treesitter query files are not recognized as such when
opened from inside their directory, because the full path returned from
fnamemodify(_, ':p') contains backslashes, while the filetype patterns
expect forward slashes.
Solution:
Normalize the result of fnamemodify(_, ':p') before trying to match it
to filetype patterns.
Co-authored-by: Justin M. Keyes <justinkz@gmail.com>