RFE: Mouse acceleration profile enhancements

Summary

Mouse acceleration that feels better subjectively than the existing profile, as agreed on by a reasonably large number of testers. Or, ability to choose between a small number of alternate acceleration profiles.

Feature details

Compared to the current mouse acceleration profile, personally I find it desirable to have:

• A greater difference in speed between slow and fast movements
  • Currently, at settings where slow movements are precise enough, fast movements aren't fast enough
  • Likewise, at settings where fast movements are fast enough, slow movements are too fast and create muscle strain
• A smoother transition (continuous?) from less to more acceleration, over velocity
  • Currently experimenting with quadratic curves instead of ramp/plateau/ramp

Affected Hardware

All mice

Implementation in Other Systems

Windows 10 with "Enhance pointer precision" on comes reasonably close to my preference on this. MacOS is slightly different subjectively, but fairly similar to Windows 10. AFAICT, current libinput differs from both of those more than they do from each other.

(@mdmayfield is currently working on a proof-of-concept for this)