Support for device specific key handlers

This is a squash commit of the following changes,
only modified for the new SDK.

  Author: Alexander Hofbauer <alex@derhofbauer.at>
  Date:   Thu Apr 12 01:24:24 2012 +0200

      Dispatch keys to a device specific key handler

      Injects a device key handler into the input path to handle additional
      keys (as found on some docks with a hardware keyboard).

      Configurable via overlay settings config_deviceKeyHandlerLib and
      config_deviceKeyHandlerClass.

      Change-Id: I6678c89c7530fdb1d4d516ba4f1d2c9e30ce79a4

  Author: Jorge Ruesga <jorge@ruesga.com>
  Date:   Thu Jan 24 02:34:49 2013 +0100

      DeviceKeyHandle: The device should consume only known keys

      When the device receive the key, only should consume it if the device
      know about the key. Otherwise, the key must be handle by the active app.
      Also make mDeviceKeyHandler private (is not useful outside this class)

      Change-Id: I4b9ea57b802e8c8c88c8b93a63d510f5952b0700
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>

  Author: Danesh Mondegarian <daneshm90@gmail.com>
  Date:   Sun Oct 20 00:34:48 2013 -0700

      DeviceKeyHandler : Allow handling keyevents while screen off

      Some devices require the keyevents to be processed while the screen
      is off, this patchset addresses that by moving the filter up in the call
      hierarchy.

      Change-Id: If71beecc81aa5e453dcd08aba72b7bea5c210590

  Author: Steve Kondik <steve@cyngn.com>
  Date:   Sun Sep 11 00:49:41 2016 -0700

      policy: Use PathClassLoader for loading the keyhandler

       * Fix crash on start due to getCacheDir throwing an exception.
       * We can't do this anymore due to the new storage/crypto in N.

      Change-Id: I28426a5df824460ebc74aa19068192adb00d4f7c

  Author: Zhao Wei Liew <zhaoweiliew@gmail.com>
  Date:   Sun Nov 20 08:20:15 2016 +0800

      PhoneWindowManager: Support multiple key handlers

      Convert the string overlay to a string-array overlay
      to allow devices to specify an array of key handlers.

      Note that the keyhandlers towards the start of the
      array take precedence when loading.

      Change-Id: Iaaab737f1501a97d7016d8d519ccf127ca059218

  Author: Paul Keith <javelinanddart@gmail.com>
  Date:   Thu Nov 23 21:47:51 2017 +0100

      fw/b: Return a KeyEvent instead of a boolean in KeyHandler

      * Allows handlers to modify the event before sending it off
        to another KeyHandler class, to handle things like rotation

      Change-Id: I481107e050f6323c5897260a5d241e64b4e031ac

Change-Id: Ie65a89cd7efd645622d99d47699df847bc3ad96b