Add the option to merge the title bar with navigation bar

[jumpy-lion]

Describe the project you are working on

A C# action 3D game.

Describe the problem or limitation you are having in your project

When Godot is opened side-by-side with another application, it would be nice, if they looked similarly. Many IDEs and probably every browser have their minimize/maximize/close buttons in the navigation bar.
Additionally, Godot's floating windows don't have their Godot icons on Linux (tested on KDE Plasma Wayland)

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Add the option to merge the title bar with navigation bar

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

If this enhancement will not be used often, can it be worked around with a few lines of script?

No trivial workaround,

Is there a reason why this should be core and not an add-on in the asset library?

It changes the core UI functionality.

[RedMser]

This already is implemented for MacOS with the Expand to Title setting: godotengine/godot#64777

Which makes this proposal a duplicate of #4846 and will be resolved by godotengine/godot#96310