Add trackball-style rotation for 3D transform gizmo

[ryevdokimov]

Closes: godotengine/godot-proposals#7753

Requires and Includes: #108608 and #108576 (these were merged)

Common functionality in other 3D software that increases the usability of the rotation gizmo.

2025-08-26.04-36-01.mp4

[michaelharmonart]

great work! now that the code is already here it might be worth looking into having this style of point on sphere projection for calculating locked rotation axis adjustments as well. (like in maya for example)

it's very intuitive to use compared to the current gizmo behavior (which will be unstable when dragging near the origin)

[KoBeWi]

The implementation looks fine (based on other gizmos).

I gave it some testing and compared it with Blender, the Blender's trackball rotation is much faster, but otherwise they seem to function the same. The old rotation mode is still available via the white rotation circle.

Note that this also changes the default free dragging behavior of Transform Mode, from move to rotate, idk which one should be preferable.