Pass onBootCompleted from SystemBars to StatusBar class

SystemBars is a wrapper class for system bar classes which implement
SystemUI class. So SystemBars should dispatch onBootCompelete event
to a Status bar classe as well as other SystemUI events.

This will benefit any custom Status bar implementation. But under
the current implementations, this affects only ARC, since on phone,
#onBootCompleted isn't overridden in the
com.android.systemui.statusbar.phone.StatusBar.

Bug: 126294007
Bug: 128876921
Test: none

Change-Id: Ib7e206da70489b1401eb2bb01bab2bc431c022eb
(cherry picked from commit 2b80e587d182adeb1bbbbc160df4624ad1d2200c)