Respect light nav bar flag set by IME on keyguard

Currently LightBarController takes care of both ScrimBehind alpha and
ScrimInFront text color when finally deciding whether light navigation
bar mode should be enabled or not.

When IME is shown on the keyguard, however, light navigation bar flag
explicitly set by the IME actually needs to be used because
ScrimController does not put anything over the IME layer in that
state.

This CL addresses the above corner case, by also forwarding ScrimState
from ScrimController to LightBarController so that LightBarController
can change the behavior when scrim UI is in bouncer mode.

Test: atest CtsInputMethodTestCases
Test: atest com.android.server.policy.PhoneWindowManagerTest
Test: atest SystemUITests:com.android.systemui.statusbar.phone.ScrimControllerTest
Test: Manually tested Manually tested with ThemedNavBarKeyboard sample
  1. make -j ThemedNavBarKeyboard
  2. adb install -r $OUT/system/app/ThemedNavBarKeyboard/ThemedNavBarKeyboard.apk
  3. adb shell ime enable com.example.android.themednavbarkeyboard/.ThemedNavBarKeyboard
  4. adb shell ime set com.example.android.themednavbarkeyboard/.ThemedNavBarKeyboard
  5. Open Dialer app
  6. Focus in the top edit field.
  7. Tap "EXTENDED LIGHT NAVIGARION BAR" mode
  8. Make sure that the navigation button color is optimized for light navigation bar
  9. Swipe down the notification shade.
 10. Make sure that the navigation button color is inverted.
Fixes: 72940586
Change-Id: I7a9001888f9b2d74c84c384b6302706da7a2b4b2