Improve error handling with separate ICanErrorListener

Error handling highlights:
- moved onError from ICanMessageListener to ICanErrorListener
- added isFatal callback argument to request client disconnect
- don't down interface that's already down

Also:
- don't crash if it's not possible to unregister ICanBus
- don't crash while trying to down interface that failed
- make hidl-utils available to vendor libraries

Bug: 143779011
Test: implemented a VHAL service prototype that communicates with this HAL
Change-Id: I98d054da9da0ead5ef952aebc086e052ac996212