[CS] Remove CentralSurfaces from OverviewProxyService; just ask shade.

Since OverviewProxyService already has access to ShadeViewController and
the CentralSurfaces methods just proxy to the shade anyway, have
OverviewProxyService ask the shade directly.

This also refactors the #onInputFocusTransfer method into three separate
methods instead of having boolean parameters.

Bug: 277764509
Test: small swipe down from launcher -> verify input focus transfer
started then cancelled
Test: fling down from launcher -> verify input focus transfer started
and completed successfully
Test: 2 finger trackpad swipe down from home on tablet -> opens shade
Test: 3 finger trackpad swipe down while in app on tablet -> opens shade
Test: atest NotificationPanelViewcontrollerTest OverviewProxyServiceTest

Change-Id: I7e2429999e4805d1ad9c239359a0bf7249050a2a