Associate starting window with task once a TF is added

Because the host activity of starting window may not be moved
into TaskFragment, and the order change from WCT is outside
the scope of transferring starting window.

Bug: 243120073
Test: atest ActivityRecordTests#testStartingWindowInTaskFragment
Change-Id: I8a052af72bf4c307e9d72e10ed47a7f8ffbdf847