Fixed a few issues around notifications and density changes

Because density and font size changes would actually be
delivered by Dependency, the SystemUI could actually get
the onDensityChanged after the onDensityOrFontScaleChanged.
Let's make sure all configuration changes now go through the
same listener.
This also ensures that the caching of the icon offsets is done
correctly, since the statusbar layout may actually be laid out
later then the shelf.

Test: change density from small to large, observe normal layout
Change-Id: I313b5334ccbb57f7929fe03dbd5119396123b137
Fixes: 35678628