Uses Configuration.uiMode in DozeMachine to determine if car mode is active

Other changes:
 - Use onConfigurationChanged instead of intents to detect when we enter/exit car mode to avoid any race conditions.
 - Renames mConfig field to mAmbientDisplayConfig.

Fixes: 254228426
Test: atest com.android.systemui.doze
Test: manual, revert ag/16853283 locally, go to AoD, run 'adb shell cmd uimode car yes', no doze triggers should wake up the device. run 'adb shell cmd uimode car no', doze triggers (tap, pickup, etc) should wake up the device.
Change-Id: I017a00ae776482f6ff329f72250bd0584961aedf