Changes to use new startTasks API

When shell transitions is enabled, this will use the
newer multi-task-launch api and control the animation.

There is no actual animation yet, this just adds the
infrastructure.

Bug: 182002789
Test: enable developer option and enter split via recents
Change-Id: If5be104a86e7b5f743f85efed20b0d2bf1b8bfd1