Move SplitscreenEventLogger to StageCoordinator

Currently, the SplitscreenEventLogger is declared as private final and
initialized in constructor of the SplitScreenController and not used
anywhere else in the SplitScreenController. Moved the initialization to
the StageCoordinator and removed the field from SplitScreenController.

Bug: 245650570
Test: atest SplitTransitionTests
Test: atest SplitScreenControllerTests
Test: atest StageCoordinatorTests

Change-Id: Iedc8893982f3bc4ba4c41f6a394f5fdf39098a99