Fix layer order of wallpaper with counter-rotator in default handler

The layer of wallpaper should always be at the bottom. Otherwise other
windows below it will be invisible during a transition animation.

Also put the same usages of CounterRotator to a new helper class.

Bug: 206094140
Test: adb shell setprop persist.debug.shell_transit 1; reboot
      atest com.android.server.wm.flicker.launch.OpenAppWarmTest
      Or use shell command "am start" to launch a landscape
      activity while wallpaper is visible in portrait.

Change-Id: Ia78450af45185782ce2268393e2a8b6bb8b4c794