Add APPEARANCE_TRANSPARENT_CAPTION_BAR_BACKGROUND

To control whether the caption bar background is opaque (default) or
fully transparent. Also adds APPEARANCE_LIGHT_CAPTION_BARS to control
the foreground color of the caption bars when the background is set
to transparent and the app will draw a background themselves.

Bug: 316387515
Flag: ACONFIG android.view.flags.customizable_window_headers
DEVELOPMENT
Test: m

Change-Id: I5413ef48b1e89b624ecbbcb10bcd735c55575193