Fixed some issues with tasks with the same affinity in different stacks

- It is possible for tasks in different stacks to have the same root
affinity. This can be an issue when we are looking for the best task to
launch an acitivty into since there can be a better match in a different
stack based on class name. We now save the task matched by root afinity
and try to find a better match by class name. If we don't find a better
match we use the match based on root affinity.
- For pinned stack we don't allow root affinity matching as no other
task should be launching in the stack based on affinity.
- Correct ASS#moveActivityToStackLocked to use the passed in stack id
instead of the PINNED_STACK_ID.

Bug: 26015860
Change-Id: I6ec44bc97bf3c669c2305a58563518cf9bfc7804