SystemUI: Add dual-tone light and dark themes for QS

Google's dual-tone QS design where the notification panel has a
semantically higher elevation adds depth to the notification+QS shade,
and we don't necessarily have to give it up just because our QS has
light and dark themes.

To preserve the dual-tone effect, use a darker background color for the
QS section:

Light:
    Notifications: neutral1 20 (surface_light)
    Notification panel: neutral1 50 (light BG)
    QS background: neutral1 100 (darker light BG / surface_header_light)
    Inactive QS tiles: neutral1 20 (surface_light)

Dark:
    Notifications: neutral1 800 (surface_dark)
    Notification panel: neutral1 900 (dark BG)
    QS background: neutral1 950 (surface_header_dark_sysui modulated to L* 5)
    Inactive QS tiles: neutral1 800 (surface_dark)

The dark QS background could be neutral1 0 (black) like it was before,
but I don't think it looks as good because it can't be tinted based on
the active wallpaper and thus stands out from other colors.

Unfortunately, Google's current CAM16-based modulation causes hue shifts
in extreme light and dark shades (e.g. L* = 98 / 5), but we'll fix this
by generating and overlaying modulated surface colors in our
ThemeOverlayController implementation.

Demo screenshots: https://twitter.com/kdrag0n/status/1445922541218922496



Change-Id: Icdc4957ecb4e0201377351f1a3e1c6928d6b3955
Signed-off-by: PainKiller3 <ninadpatil100@gmail.com>
Signed-off-by: Saalim Quadri <danascape@gmail.com>