Play common transition animations from a common method.

There are 3 animations that 3 different transitions use; to prevent
future problems, let's put them all in one place. For instance,
ag/781127 added dispatchOnLauncherTransitionStepAnim() to the two
transitions that existed in burnaby-polish, but not to a third,
startAnimationToNewWorkspaceState(), that was added in master. If a
common method existed in polish, the new animation would have merged
into master automatically instead of forcing us to remember to add it.

Change-Id: I7775aaa43a08ae8b8241b0eeb77b6c84167c5ff0