Modify callback for delivery reports to match incoming messages

From #2832862-7: Automatic incoming route creation →

Some of the ideas from #2832862: Automatic incoming route creation → could be applied to the incoming reports endpoint as well:

• Change \Drupal\sms\Plugin\SmsGatewayPluginInterface::parseDeliveryReports to \Drupal\sms\Plugin\SmsGateway\SmsGatewayPluginInterface::processReports
• Change above method to a controller response / one without required arguments and interface.
• Require response object to be created inside the above method.
• Recycle the \Drupal\sms\SmsProcessingResponse object from this issue, adding a new g/setReports method to that object.
• \Drupal\sms\Provider\DefaultSmsProvider::processDeliveryReport can be reworked to just take report objects, instead of needing to handle a HTTP request.
• Add a incoming reports route specific "_route" annotation. Separates incoming reports capability annotation.