Set DigitalWellBeingToast to GONE when there is no limit

- Surprisingly swithcing between GONE and VISIBLE doesn't cause a jank when swiping up
- Having DigitalWellBeingToast GONE should reduce the amount of time to layout RecentsView when there is no banner, which should fix b/364621823
- It might or might not reduce memory usage in b/364568201
- Also add missing accessibiltiy node for DigitalWellBeingToast

Bug: 364621823
Test: Swipe up with the app having DWB banner in different index, no jank when landing to Overivew
Flag: EXEMPT BUG_FIX
Change-Id: Ibf5a7f5318de509fe572779dd774dce71881aabe