[Feature Request] Allow 'external-only' display mode while docked

Describe your issue

What's the expected behaviour?

When I plug my PinePhone CE into its convergence adapter, I would like to disable the touch screen (I don't have a nice way of even viewing it anyway -- no clever mounting bracket exists to my knowledge).

What's the current behaviour?

I cannot use the external display only while docking my PinePhone. Application windows regularly open on the phone display and the squeekboard keyboard pops up (relatively bright distracting light) whenever I select a text field (separate issue)

How to reproduce your issue?

  1. Connect your PinePhone to its Convergence Adapter (only some models)
  2. Connect HDMI on a supporting version of pmos (recent update)
  3. Attempt to disable phone display

What device are you using?

PinePhone CE PMOS Edition

On what postmarketOS version did you encounter the issue?

  • edge (master branch)
  • stable (v20.05 branch)

On what environment did you encounter the issue?

Phone environments

  • Phosh
  • Plasma Mobile
  • Sxmo

Other

  • No environment
  • GNOME
  • KDE Plasma
  • Kodi
  • MATE
  • Shelli
  • Sway
  • Weston
  • Xfce4
  • fbkeyboard
  • i3wm

How did you get postmarketOS image?

What's the build date of the image? (in yyyy-mm-dd format)

Additional information