Fix talkback in split mode

1. Announce description of both snapshot in GroupedTaskView.
2. Announce them in correct order.

After setting right content description for both the apps in split mode, announcement order was reverse. Seems that order of the node tree which android sees was wrong. Also order did not change even in RTL mode.

see here https://paste.googleplex.com/6492038621298688.

The correct order is manually set using addChildrenForAccessibility in GroupedTaskView. (similarly being used in RecentsView since we use reverse order for overview). Also considered RTL.
See order after fix here
https://paste.googleplex.com/6492038621298688

https://drive.google.com/file/d/1BA1YKkcNsovEu4us9cvq5xOdXviTR1OV/view?usp=drive_link

Other alternatives tried were fixing order using android:accessibilityTraversalAfter and android:accessibilityTraversalBefore, both in layout and programatically which doesn't seem to work.

Test: Manual - Using Node tree debugging of talkback developer options.(Print and filter by tag TreeDebug)
BUG: 330424779
Flag: EXEMPT bugfix
Change-Id: If3c360277bd951d2d2b223bab7844e078e9c7d27