Mouse lock for trackball mode

[parkerlreed]

Is your feature request related to a problem? Please describe.
Currently, when trackball mode is enabled, the drag interaction is limited by the window/screen bounds.

Describe the solution you'd like
Mouse lock when trackball mode is enabled, enabling continuous movement with a trackball/mouse, not limited by the bounds of the container.

Describe alternatives you've considered
Tried looking for something in KDE Plasma/Gamescope that could do this but seemingly nothing exists.

Additional context
Was thinking possibly a relative mouse capture similar to how games handle mouse input.

Contribution
Can help test but wouldn't know where to start in implementing.

[mwestphal]

Not sure VTK can do that, investigation needed.