Allow making SpinBox buttons horizontally laid out rather than vertically

[mieldepoche]

Currently, SpinBox has two vertically stacked buttons to increment/decrement the value. However, this makes them very small and tedious to aim at, or at least harder than it needs to be.

I have been using inkscape in the past few days, and look at that: taller, easier-to-aim-at buttons!

SpinBox in godot	in inkscape

I prefer those ones a lot. I think they're easier to hit, and in practice I don't think they would eat up precious space: do people ever export ints so large they fill up the line?
The current style could still apply when lacking space or if the SpinBox is too small or if the user chooses so, but I believe the editor would benefit from that improvement since most of its spinboxes (inspector and project settings) are usually wide.

I compressed the column a bit in my inspector to make a point:

I think there's room for another button in there, and 5 digits would fit in a very compressed column.

rough mockup, and size comparison:

as you can see, this is sacrificing display space for usability.
Again, I don't know if someone with a tiny monitor ever needed to input a 10-digits value in a spinbox, which is why I believe this would be a good editor usability improvement.

as a side note, using actual buttons nodes would provide the benefit of mouse-hover and click feedback, which is so subtle in godot it might as well not happen, but feels good in inkscape:

simplescreenrecorder-2024-04-08_16.16.39.mp4

[AThousandShips]

This should be configurable, rather than changed completely, the ability of SpinBox to be used in narrow forms is important

[Shadowblitz16]

Also stuff like this...
< 0 >
instead of just this...
0 -+

[Mickeon]

It's not quite the same, but the more styling options of godotengine/godot#89265 may help make this a reality.