Improve window resizing to use the default clear color as a background instead of black during the resize operation

### Tested versions

Godot version: v4.5.stable.official.876b29033

I don't rememeber this happening in older versions. I didn't use Godot since around 4.1, though.

### System information

Xubuntu 22.04.5 LTS - Godot v4.5.stable - AMD Mesa 23.2.1

### Issue description

Resizing the game window is glitched, both in how it resizes (it "snaps" back and forth) and in the window's content (artifacts).

https://github.com/user-attachments/assets/482e5b74-2fc7-4fc3-bcbc-d02a06355b24

### Steps to reproduce

Steps:

- run any project.

Godot version: v4.5.stable.official.876b29033

Godot project: Renderer: *Compatibility*, but _Forward_ is the same.

Xubuntu 22.04.5 LTS (Xfce)

GPU: Radeon RX 570 ITX 4G GDDR5

```
> echo $XDG_SESSION_TYPE
x11
> dmesg | grep amdgpu
[drm] Initialized amdgpu 3.57.0 20150101
> glxinfo | grep "OpenGL version"
OpenGL version string: 4.6 (Compatibility Profile) Mesa 23.2.1-1ubuntu3.1~22.04.3
```

This doesn't happen on my Windows machine.

### Minimal reproduction project (MRP)

Any default new Godot project.

Start with any default Godot project using the Compatibility renderer on Xubuntu 22.04.5 under X11 and reproduce the resize snapping and content artifacts described in the attached video. Compare the behavior with Windows; done means resizing no longer snaps or leaves artifacts and uses the default clear color instead of black during the operation.

Written by the indexing model from the issue text.