Saves a specific resource type to a file. The engine can save resources when you do it from the editor, or when you call [method ResourceSaver.save]. This is accomplished with multiple [code]ResourceFormatSaver[/code]s, each handling its own format. By default, Godot saves resources as [code].tres[/code], [code].res[/code] or another built-in format, but you can choose to create your own format by extending this class. You should give it a global class name with [code]class_name[/code] for it to be registered. You may as well implement a [ResourceFormatLoader]. Gets the list of extensions for files this saver is able to write. Returns [code]true[/code] if the given resource object can be saved by this saver. Saves the given resource object to a file. [code]flags[/code] is a bitmask composed with [code]FLAG_*[/code] constants defined in [ResourceSaver]. Returns [code]OK[/code] on success, or an [code]ERR_*[/code] constant listed in [@GlobalScope] if it failed.