Fix D3D12 looking blurry in the editor at fullscreen.

[blueskythlikesclouds]

Fixes #113634.

The window resolution without the transparent border is passed to the rendering drivers, but Vulkan and OpenGL force it to the actual window resolution anyway. D3D12 is the only one that actually respects it, but this ends up causing the swap chain to be stretched horizontally by 2 pixels. The behavior can be made consistent across all the rendering drivers by simply passing the actual window resolution.

[Zireael07]

Might be worth it to add a comment explaining what off_x is and why it NEEDS to be added in all 3 renderers, so that the issue does not sneakily come back in some "cleanup pass"

[Repiteo]

Thanks!