applets/systemtray: allow fully disabling app SNIs
Reason for the change
Some people don't like app-provided SNIs (Status Notifier Items, AKA "tray icons"), but some apps don't offer an option internally to disable their SNIs. This is annoying.
As such, offer the option to hide app-provided SNIs from the System Tray.
When the user does this, a message will be shown warning them that it's at their own risk since it could break the app.
Implementation-wise, the cleanest way I found was to save the list of
disabled SNIs in a new config file key, rather than adding them to the
existing extraItems key; extraItems was designed to only hold plasmoid
IDs, and re-engineering it to accept SNI IDs as well ended up being
much more complex and fragile.
Test plan
- Launch Discord or another annying app that doesn't allow disabling its tray icon in the app's own settings
- System tray arrow > settings button > the app in question > visibility: disabled
Restart plasmashell to make sure it worked
Do the same for the other visibility values.
Screenshots or screen recordings
Bugs fixed
FEATURE: 489239
FEATURE: 470798
FIXED-IN: 6.4.0