[Feature] Add support for being a feed source for launchers

[mpeter50]

Describe the solution you'd like

Nowadays a lot of launchers, including phone's preinstalled ones, have a feature that allows inserting a news feed or some other kind of menu on a dedicated page of the system launcher. Most often this is a Google Discover feed, and unfortunately its often not configurable, but launchers like Lawnchair let you select the app that will be shown there.

According to this issue at the Lawnchair repository, for becoming a launcher feed source you need to implement a DrawerOverlayService in your app. In my understanding this you can show your own UI in one of the launcher pages. An example implementation is HomeFeeder, another is its fork Neo-Feed, both of which I think is a Google Discover source but provided by a FOSS app.

The implementation could show a similar list of news items like the app's main screen does, but perhaps with a short quote from the beginning of the article, and an image if the article has one.

Describe alternatives you've considered

Alternatively users can use the DisoverKiller Xposed module, which should be able to repalce the default Discover feed in launchers with any app.

However, this requires heavy modification of the system, which can be fragile, and which could also make banking and other apps to refuse basic operation. People also argue that using Xposed significantly reduces the system's security, which is true both because of its capabilites, but also because on virtually all phones you cant use Xposed with a locked bootloader.