Full touchscreen support

[v6ak]

An umbrella issue what is needed for full touschscreen support.

Implementation

• #2281 input proxy support
• Qubes has at least one touch-friendly DE (e.g., #1806 or Android GUIVM)
• Support in guests: #3337

Checks

• Touches work well with multi-monitor setup when using some touch-friendly DE and input proxy – regardless of screen positions and primary/secondary screen status. (It might require no implementation, but it should be verified if it works well. See #2281 (comment) for more details.)

Bonus

• Optional: Touchegg or something similar for multitouch gestures.

Notes on desktop environment

According to https://laptop.ninja/the-best-linux-distributions-for-touchscreens/ , the best DE for touchscreen are Gnome 3 and Unity. Since Unity is probably dead, Gnome Shell looks reasonable. (It might change if some active community resurrects it.) They suggest using touchegg, I am adding it on the list. Android GUIVM could be interesting, but it is probably not the easiest way to go.