Rotation axes are not hoverable/selectable when camera look vector is in-plane with the arc

[Aeledfyr]

Tested in the web demo, but also occurs in transform-gizmo-egui 0.3.0.

The selectable area of the arc-based rotation controls appears to depend on the angle from the camera; when the arc is in-plane with the camera's look vector, the selectable area is effectively zero. (That is, when the arc appears as a straight line in the view.)

Example when the arc is in-plane, where it doesn't recognize hover:

Example when the arc is slightly out-of-plane, where selection does work:

Note that I'm testing this on a high-dpi display, so that may affect the minimum width of the arc, but it shouldn't influence how the width changes as the camera angle changes.

[urholaukkarinen]

The current rotation arc picking implementation is a bit poor and does not work properly with steep angles. I'd like to re-implement it at some point