Resize boot animation on display changes

Use DisplayEventReceiver to listen for display hotplug
events and resize the boot animation is display size
changes.

Bug: 156448328
Test: manually make sure the boot animation has correct
dimensions in the following cases
     I. With boot animation file
        1. scrcpy
        2. start boot animation with
              adb shell /system/bin/bootanimation
	   when no physical display is connected (= 480p
           fake HWC display). Use the virtual display from
           scrcpy to check the boot animation size.
        3. connect a 1080p display
           (HWC sends hotplug connect to change the display)
        4. disconnect the real display
     II. Same steps without boot animation file
         (android logo should be displayed)

Change-Id: Ib3f0383686399669e8de10456092baaec607fa01