Minimize API of KeyguardBottomAreaView

As part of the effort to refactor KBAV to a more modern implementation,
this CL minimizes the public API surface of that class.

There are namely three changes:
1. Removal of setCentralSurfaces (this was no longer used inside KBAV)
2. Unification of the four "init" methods into one
3. Making startFinishDozeAnimation private (it was not called from
   outside the class)

Bug: b/235403546
Test: built using make and verified the bottom view is visible on the
lock screen. Does the bouncy animation, opens the home controls view
from that button, shows the song ID, etc.

Change-Id: I7393d357e82a139c3ad83b2f48b0f2dc9a02b93a