Initially we did this to avoid a duplicated task right after the migration from Fennec. We'd end up
with the original task from Fennec and the new one from Fenix; with the Fennec task still showing
Fennec in the app switcher, but launching Fenix once selected.
Anyhow, now on Android 11 this causes the Fenix task to get duplicated. The simple fix is to not
do any of that anymore. This may re-introduce the problem with the Fennec migration, but:
* We are at 100% rollout for quite some time. There are still users migrating, but the impact
of the bug is much lower.
* The bug after the migration was only temporary. This bug here is happening every time you
launch Fenix. So I'd rather fix this than a possible inconvenience right after the migration.
Reusing the same taskAffinity makes sure that we are launching into a potentially already
existing task from Fennec. Without that we may spawn a new task and will show up twice
in "Recent apps" - with one entry still having a fennec screenshot.
* With this patch fenix build variants will launch HomeActivity directly from the launcher.
This will get rid of the performance regression outlined in #7818.
* Fennec build variants will launch into MigrationDecisionActivity which will show the
migration UI or launch normally into the app. This is faster than going through
IntentReceiverActivity (measured and perceived).
