Make display/window/strectch/mode default to canvas_items

[ObaniGemini]

Is there a reason why you would want 2D elements to not scale with the window by default?

It sounds like the canvas_items mode would be more fitting in default configs, I don't see a reason to use disabled in a standard game use case.

[Calinou]

Thanks for the proposal! Consolidating in #3939.

Is there a reason why you would want 2D elements to not scale with the window by default?

Non-game applications generally want that behavior.