Let light bar state be able to be read by insets API

Before this CL, if the light bar state is controlled by the window style
attribute, apps can only query it via View#getSystemUiVisibility.
However, the API has been deprecated since Android SDK 30.
WindowInsetsController#getSystemBarsAppearance could only return the
values set by WindowInsetsController#setSystemBarsAppearance. Thus, no
API (except the deprecated one), can return the light bar state.

This CL adds a new @hide method, setSystemBarsAppearanceFromResource.
The light bar state read from resource will be passed to that method.
And now getSystemBarsAppearance will also return the appearance flag
specified via setSystemBarsAppearanceFromResource if the same flag is
not controlled by setSystemBarsAppearance.

Fix: 330891999
Flag: NA
Test: atest PendingInsetsControllerTest ViewRootImplTest
Test: ThemeSystemBarsTest
Change-Id: If740d360ad3211b682bd04598099240863048960