Replace old app transition type to new transition type (1/N)

- Rename TransitionType to TransitionOldType, and define a new
  TransitionType.
- Calls prepareAppTransition which takes a new TransitionType when app
  transition related event happens.

The TransitionOldType and related logic will eventually removed. Until
migration finishes, we keep both.

Bug: 166736358
Test: Pass existing tests, since no new logic is enabled.

Change-Id: I984f68d5ecfae56fbfe7d91babbfddcf34378f6c