Adds an Assistant handle controller to the AssistManager

This will control when the Assistant handles show or hide.

Change mode using the following command:

$ adb shell am broadcast \
  -a "com.google.systemui.SET_ASSIST_HANDLE_BEHAVIOR" \
  --es behavior "${BEHAVIOR}"

BEHAVIOR can be one of: OFF, LIKE_HOME, or REMINDER_EXP

Change the minimum time between handle appearance in REMINDER_EXP using
the following command:

$ adb shell setprop ASSIST_HANDLES_SHOWN_FREQUENCY_THRESHOLD_MS \
  ${DESIRED_MILLISECONDS}

Change the duration the handles appear in REMINDER_EXP using the
following command:

$ adb shell setprop ASSIST_HANDLES_SHOW_AND_GO_DURATION_MS \
  ${DESIRED_MILLISECONDS}

BUG:132983599
BUG:131115187
Test: atest AssistHandleBehaviorControllerTest
Test: Tested locally.
Change-Id: I44bb59367159226b67a2aeb49aae2a5b34584d70