Re-introduced fullscreen and added decorated for Gtk4

[WebReflection]

This MR exports two extra symbols to remove decorations (chromeless) and to provide an easy way to make the window full screen.

A new SizeHint.FULLSCREEN can be used to provide such hint while the Size now has a decorated value which, if false, would remove all decorations around the UI.

Related webview changes https://github.com/WebReflection/webview/pull/1

Published on npm as @webreflection/webview-bun