Change Camera3D gizmo shape according to viewport size

[timothyqiu]

It's currently always a square.

The aspect ratio could match the viewport aspect ratio.

[Calinou]

Feel free to open a pull request for this 🙂

Note that whenever the viewport width/height project setting is changed, gizmos need to be updated. The project's width/height aspect ratio should be used, not the editor window's aspect ratio.

[akien-mga]

Implemented by godotengine/godot#68682.