handle map layer values
These are treated as the file path to the layer.
E.g.
base_file_name(@some_variable_which_is_a_layer)
will return the base file name of the layer's source
base_file_name: Returns the base name of the file without the directory or file suffix.
file_exists: Returns true if a file exists
file_name: Returns the file name from a full path
file_path: Returns the directory/path from a full file path
file_size: Returns a file size
file_suffix: Returns a files suffix/extension
is_directory: Returns true if a file path is a directory
is_file: Returns true if a file path is a file
