SystemUI: add double tap to sleep gesture

Based on the following squashed changes, forward-ported to Oreo
and adapted to the Lineage SDK:

Author: Roman Birg <roman@cyngn.com>
Date:   Sun Nov 23 06:54:06 2014 -0800

    SystemUI: double tap to sleep improvements

    * Make it more reliable
    * Add it to keyguard
    * Add a content observer to not always query Settings.System on every
    touch event

    Change-Id: I292c4d9d9f810843590b7a9ec6e15b99ac44009d
Signed-off-by: Roman Birg <roman@cyngn.com>

Author: Adnan Begovic <adnan@cyngn.com>
Date:   Wed Nov 11 12:05:59 2015 -0800

    fw: Move DOUBLE_TAP_SLEEP_GESTURE to CMSettings.

    Change-Id: I8274b7c241cef6835a1114a702e68c95b6d2e036

Author: Zhao Wei Liew <zhaoweiliew@gmail.com>
Date:   Fri Oct 7 08:56:25 2016 +0800

    SystemUI: Use Tuner API for CM settings

    Get rid of all the excess code by implementing TunerService.Tunable
    and observing any changes made to the settings through it.

    Remove UserContentObserver as the Tuner API handles user switches.

    Also remove some unused imports that were introduced in earlier
    CM commits, but were never removed since.

    Change-Id: Iecafafabdaec82b3b3c72293bea865de48f0e90a

Author: Altaf-Mahdi <altaf.mahdi@gmail.com>
Date:   Wed Nov 11 16:07:49 2015 -0500

    Double tap to sleep anywhere on the lock screen [1/3]

    Change-Id: I7dd46f3fafeb2e629974c0f32083d4d9774fb1de
    [neo: Using Tuner API.]
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>

Change-Id: Ic1a40d4340890905de2631c666270e81c390d261