Editor popup position offset when popped up in area covered by Taskbar on Windows in fullscreen

### Tested versions

Reproduced in:
- v4.2.2.stable.official [15073afe3]
- v4.3.stable.official [77dcf97d8]
- v4.4.dev3.official [f4af8201b]

### System information

Godot v4.4.dev3 - Windows 10.0.19045 - Multi-window, 3 monitors - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 2070 SUPER (NVIDIA; 32.0.15.6094) - AMD Ryzen 9 5950X 16-Core Processor (32 threads)

### Issue description

In fullscreen mode editor, any popup showing up will avoid the taskbar area as if the Taskbar is still there. This happens both when the taskbar is vertical or horizontal, though it's mainly an issue with vertical taskbar because those frequently used popup menus will be offset.

Edit: The problem goes away in single windowed mode.


### Steps to reproduce

1. Create new project.
2. Switch editor to fullscreen mode with shortcut Shift + F11.
3. Hover over tabs in the bottom dock with the taskbar at the bottom, or click the "Scene" menu in the menu bar with the taskbar at the left.
4. See how tooltips and popup menus are misplaced. A large taskbar will make it obvious.

### Minimal reproduction project (MRP)

N/A

Reproduce the issue in the Godot editor on Windows using Shift + F11, with vertical and horizontal taskbars and multi-window mode. Trace the fullscreen editor's popup and tooltip positioning, then verify that menus and tooltips are aligned correctly without the taskbar offset while preserving the reported single-windowed behavior.

Written by the indexing model from the issue text.