[ExploreByTouchHelper] Make a11y calls on views

Make a11y calls on the views in ExploreByTouchHelper instead of on
the delegate itself. This makes it consistent with the support
library implementation and allows to use this helper on views that
implement custom accessibility methods. (Like TextView)

Change-Id: I6b0d94cecb752289394272dfcf9bd6f55f9700d9