Blender Git Loki

Transform Manipulator: Rotation indicator (arc overlay)

Adds a arc shaped overlay indicating the current rotation value for the rotation transform manipulator.

This is still ignoring constraints, which can be fixed by calculating angle using object matrices instead of cursor position.
Seems like we could also use BLI_dial_angle here, but will check on that at some other point.
Visual design is a subject to change of course. Will add screenshots to T47032.