Starts the dictation recognization session. Dictation recognizer can only be started if PhraseRecognitionSystem is not running.
DictationRecognizer requires that dictation is permitted in the user's Speech privacy policy (Settings->Privacy->Speech, inking & typing). If dictation is not enabled, DictationRecognizer will fail on Start. Developers can handle this failure in an app-specific way by providing a DictationError delegate and testing for SPERR_SPEECH_PRIVACY_POLICY_NOT_ACCEPTED (0x80045509).