Allow get_file_path_from_theme filterable like get_theme_file_path

[Rahe]

Hello,

I've noticed that get_theme_file_path is not used into WP_Theme_JSON_Resolver but WP_Theme_JSON_Resolver::get_file_path_from_theme method.

Since the function get_theme_file_path is filterable and to be consistent with it, I think this can be a good idea to add a filter to this method.