Fix issue with floating tasks being tracked as a drag running task

- Ignore floating tasks when calculating the "running" task for
  drag and drop purposes (since it will be used to determine the
  drag split layout, which isn't affected by floating tasks). Until
  we have a proper task repository/visible task tracking, just fetch
  a few more tasks to ensure that we actually resolve a non-floating
  task.

Fixes: 370659212
Flag: EXEMPT bugfix
Test: atest WMShellUnitTests
Change-Id: Ie9588c66a8687f8a4a5185e17f63dbe303322c54