Wayland: Support Qt::Tool, Qt::WindowStaysOnTopHint and Qt::WindowDoesNotAcceptFocus

It's possible to do a Picture-in-Picture window on other platforms with the following set of flags (basically an always-on-top window not accepting focus and not enumerated on taskbar/dock):
 

	setWindowFlags(Qt::Tool
		| Qt::WindowStaysOnTopHint
		| Qt::FramelessWindowHint
		| Qt::WindowDoesNotAcceptFocus);
	setAttribute(Qt::WA_ShowWithoutActivating);
	setAttribute(Qt::WA_MacAlwaysShowToolWindow);
	setAttribute(Qt::WA_NoSystemBackground);
	setAttribute(Qt::WA_TranslucentBackground);

But nothing seem to work on Wayland. It seems Qt has to support xdg-pip for the same functionality on Wayland. It's already supported by KDE and Firefox.

https://blogs.kde.org/2025/06/14/this-week-in-plasma-wayland-pip-and-accessibility/
https://bugzilla.mozilla.org/show_bug.cgi?id=1970372