Background crashed apps are not removed from WM hierarchy

- In Automotive portrait UI, there can be multiple tasks inside a root
  task as well. Instead of checking for all the root tasks, check for
all leaf tasks.
- When some non visible activity crashes in the background, the activity
  record is not updated and is not removed from the WM hierarchy.

Bug: 327676365

Test: m
Test: Open NDO application -> Put car in driving mode -> Crash the NDO
app. The process with its ActivityRecord should be removed.

Change-Id: Ie27dc106d938bf84ce22148e7cabceb8f13e35d9