New "App (not) in recents" constraint

[mininmobile]

Developer TODO (don't remove)

• [ ] create new branch. put issue number at start of name
• [ ] update documentation
• [ ] merge and delete branch (don't squash because want commit history to see why I made changes)

what

i would like to be able to constrain actions depending on whether an app is open in the background or not. specifically "background" as in the state where i can see it in the recents menu, not when some minor background service belonging to that app is running

why

i have my bixby button (which acts as the menu button on lineage os) remapped to act as media play/pause and i don't want this action to start playing music in my pocket when i purposefully closed my media player

using the "media is playing" constraint does not do what i want as it only lets me pause media but not resume it

also i believe it wouldn't take too long to implement ^^