Fix renaming nodes on X11

[dsnopek]

Fixes #97211

This effectively reverts PR #93682 and PR #96829, and takes a completely different approach at fixing issue #88847.

The fix here is much simpler. It looks like the issue with _window_focus_check() in that case was just that we were only checking if the main windows had input focus, but weren't also checking the XIM windows.

I've tested this on:

• i3 (on both Ubuntu 22.04 and Fedora 40)
• GNOME (both XOrg and XWayland on Fedora 40)

Testing the following issues / use cases

• Switching focus away from the project manager (was issue Godot project manager continuously steals focus on i3 #95824)
• Renaming nodes in the scene tree via F2 (was issue Renaming nodes broken on X11 #97211)
• Opening "Find in Files" via CTRL+SHIFT+F (was issue Text editor steals focus from "Find in Files" dialog #88847)
• Pressing F1 while in the code editor (was brought up on PR Fix project manager stealing focus on i3 #96829)

I'm going to try to get an environment going to test XFCE (for testing issue #74378) and KDE as well. If anyone else has access to another environment help testing would be appreciated!

[akien-mga]

Tested on KDE Plasma on Wayland (running the X11 version of Godot) and it seems to work well :)

[akien-mga]

Thanks!