Blender Git Loki

3DView: Use "real" angle for viewport roll

Since its introduction in {rB5c569d227b64}, the view roll was based on
horizontal movement only. Using a "real" angle not only feels more
natural but also has the benefit of getting more precission the further
away from the center you are (just like regular rotation, brush/stencil
rotation etc.). A similar thing has already been implemented in the
Grease Pencil Tools Addon, now make the blender standard roll the same.

Since this is not using the transform system, we are still lacking a
line in the viewport (this could be added but since this is always based
on the center of the view we dont necessarily need this), as well as the
additional Shift-extra-precission behavior.

Fixes T89883

Maniphest Tasks: T89883

Differential Revision: https://developer.blender.org/D12582