[Windows] Flickering and/or excessive slowdown in editor subwindows

### Tested versions

Godot Engine v4.3.stable.steam
Did not occur in the same project on previous 4.X versions

### System information

Godot v4.3.stable (77dcf97d8) - Windows 10.0.22631 - Vulkan (Forward+) - dedicated AMD Radeon RX 6700 (Advanced Micro Devices, Inc.; 32.0.12033.1030) - AMD Ryzen 7 3800X 8-Core Processor (16 Threads)

### Issue description

Ragged black flickering bars obscuring the top half the screen whenever a suibwindow is open OR sub 1fps performance with a subwindow open.
Flickering is more common.
Node picker, colour picker, file dialogue etc all trigger it. Seems to be editor only.
Flickering occasionally shows up right after startup.
Happens in 2D and 3D scenes.
Seemingly the poor performance and the black flickering cannot happen at the same time; restarting the editor will usually but not always flip from performance problem to flickering.

### Steps to reproduce

Open a sub window (node picker, colour picker, file picker etc) in seemingly any context.
In rare cases, opening the subwindow will tank performance to below 1 frame per second until i minimise godot or close the subwindow.

### Minimal reproduction project (MRP)

n/a

Reproduce the issue in the Godot 4.3 editor on Windows 10 with Vulkan and the reported AMD Radeon RX 6700, using the node, colour, and file picker subwindows. Compare the black flickering and sub-1 FPS cases across 2D and 3D scenes; done means editor subwindows no longer flicker or cause severe slowdown.

Written by the indexing model from the issue text.