Allow tearing / scanout with subsurface-based renderers

[vaxerski]

Discussion link

https://github.com/hyprwm/Hyprland/discussions/10396

Description

Some apps, notably browsers, but apparently also winewayland, use a single, full-frame subsurface to render their content.

This will not allow tearing / scanout to happen as surface number is checked to be 1.

We should probably check for this case, and allow both if we have a single, opaque, full-frame subsurface.