Fix adjacent task positioning for consecutive swipe gestures

- Always use the recents scale down animation when coming from BACKGROUND_APP state
- Adjust scale down animation to calculate based on translationY = 0 instead of
  translationY > 0 if it is still set from a previous interaction
- Fallback to using launcher's insets in the case that a task doesn't yet have
  thumbnail data (we remove the data when the task stack is invisible, so it
  might not yet be restored if you swipe up again too quickly)

Bug: 111926330
Change-Id: I4bf0bf1b2fa564f0a2c27e7c053c2216856cb024