Need ways to detect adaptive apps from desktop file

when thinking about adaptive we want to have

1. apps installed that work in desktop-mode, e.g. libre office
2. apps installed that work in both desktop and phone mode: epiphany, chatty, calls, ...
3. maybe have apps that are limited to phone mode

identifying these application types allows us to show clean menus in desktop and phone mode.

Since there's no point in showing apps from 1. with no external screen attached we need to somehow tag adaptive apps to avoid clutter like librem5-base!65 (merged) in the future.

One way would be to tag convergent apps with X-Adaptive: true in the .desktop file and only these show up in the menu in phone mode. Possible problems with that:

• webapps from epiphany won't have that tag (but that could be fixed)
• kirigami and apps based on other toolkits would need to use that as well

we might end up having to whitelist some apps until upstream catches up patch downstream. in the long run we want to extend the freedesktop.org spec i assume.

/cc @adrien.plazas @tobias.bernard @francois.techene if this makes sense in their plans of convergence? /cc @dorota.czaplejewicz @david.boddie since this might have been a topic in dicussions with plamo?