Always show caption in freeform even if apps are requesting immersive

The caption view visibility prior to this change was synced to the
status bar visibility because the App Handle should not be shown when in
immersive mode. However, when in freeform, InsetsState may still briefly
report an invisible status bar even though the status bar is
forcibly-shown in the desktop. For this reason, the App Header would
sometimes be removed to follow the (incorrect) status bar inset source.
This change forces the caption view to always be shown in freeform mode,
regardless of if the status bar is reported as not visible.

Flag: EXEMPT bugfix
Bug: 356405803
Test: open immersive app in freeform (e.g. Call of Duty), launch Gmail
on top, verify App Headers dont disappear (briefly or indefinitely).

Change-Id: I27dd7952e9e5b783eea6217df1e84c9053a72fab