[Status Bar Refactor] Move some PanelView setters + getters into...

[Status Bar Refactor] Move some PanelView setters + getters into PanelViewController and out of PanelBar.

PanelBar and PanelView are unrelated (despite their names): PanelBar
represents the status bar view, and PanelView represents the
notification panel. So, methods regarding PanelView shouldn't live in
PanelBar. This CL moves some of those methods out of PanelBar and into
to PanelView's controller.

Note: These methods are all intertwined, so they all need to be in 1 CL.

Specific changes:
- #shouldPanelBeVisible moved out of PanelBar into PanelViewController.
- #setBouncerShowing moved out of PanelBar into StatusBar. That
 method adjusts visibility and accessibility for both PanelBar and
 PanelView, so it shouldn't live in PanelViewController (which is
 specific to PanelView only). StatusBar seemed like a semi-logical place
 for it.
- #setHeadsUpVisible is no longer needed in PanelBar since it was only
 used to determine PanelView's visibility. Logic is moved to
 PanelViewController instead.
- StatusBar uses PanelViewController to get expansionFraction and
 isExpanded values, instead of PanelBar.

Test: 1) Modify display size while a heads up notification is showing and verify that the HUN remains visible
and the status bar updates appropriately. 2) Rotate device while
HUN is showing, same verification steps. (This tests no regression of
b/80224819.)
Test: Modify font size while the shade is open using `adb shell settings
put system font_scale 0.8`. (This approximately tests no
regression of b/110530608, since the repro steps in that bug are no
longer applicable.)
Test: atest SystemUITests

Bug: 200063118
Change-Id: Idd9715992792b20002716332ccd7c15369183b5c