Combine output_by_name and output_by_identifier

This combines `output_by_name` and `output_by_identifier` into a single
function called `output_by_name_or_id`. This allows for output
identifiers to be used in all commands, simplifies the logic of the
callers, and is more efficient since worst case is a single pass through
the output list.

sway/commands/move.c

@@ -64,7 +64,7 @@ static struct sway_output *output_in_direction(const char *direction_string,
 		}
 	}
 
-	return output_by_name(direction_string);
+	return output_by_name_or_id(direction_string);
 }
 
 static bool is_parallel(enum sway_container_layout layout,