Revert "Removing TaskFragment token from LaunchActivityItem"

This reverts commit 6dc12402
in tm-dev. The revert is necessary because SplitController
needs to access the initial task fragment token from the
activity client to ensure that split info callbacks are sent
before an activity is created.

Test: existing tests pass
Bug: b/218791665
Change-Id: I7d6506312b46af026ec19e4aad9d0f31482e175a