Do not consider embedded task as task switch

For example:
 Task A - TaskFragment - Activity X
        - TaskFragment - Task B (embedded) - Activity Y
If Y starts Activity Z in Task B, even if A and B are different,
we don't want to show starting window because B is a part of A
from user's perspective.

Bug: 197595621
Test: Start activity from embedded task fragment to the same
      task fragment.
Change-Id: I9ec40e77b675c857f46747babd3144b2989042f6