Borderless fullscreen doesn't take up the whole screen

Borderless fullscreen isn’t fullscreen. The taskbar is still showing and there is a gap above the window.

This behavior was introduced in 26.3 Pre-Release 2. It happens on both OpenGL and Vulkan.

This only happens when the window is maximized to begin with.

Steps to reproduce:

1. Maximize the window

2. Make sure Exclusive Fullscreen is off

3. Toggle fullscreen