Support different task icon margin for grid tasks

- Focused and non focused grid now have differnt margin between icon and snapshot
- The overall margin above snapshot is still the same
- Invoke updateChildTaskOrientations when focus task changes to update the margin
- Also lowered the row spacing according to spec

Bug: 194194694
Test: manual
Change-Id: I25267bef19d5a8b1dc1cf96fc1babdc3ebc39330