Move overview component logic from OverviewCommandHelper

OverviewCommandHelper previously managed both updating the current
overview component and interfacing inputs to switch to the
overview activity. This CL splits out the former to a separate
class so that the responsibilities are more focused and the code
can be reused more easily.

Test: Manual test NexusLauncher, Launcher3QuickStepGo by switching to
overview
Change-Id: I4e90918703f351d235f3cb0a45079cbb31b753ab