Speech: Public API for the language detection and switching features

onLanguageDetection callback method is added to IRecognitionListener
aidl, and is to be called when the language detection (and switching)
results are available. This callback method can be invoked on any
number of occasions at any time between the beginning and the end of
speech, depending on the speech recognition service implementation.

The following entities are created for the language detection feature:
 - `android.speech.extra.ENABLE_LANGUAGE_DETECTION`
 and `android.speech.extra.LANGUAGE_DETECTION_ALLOWED_LANGUAGES`
 key entries for the RecognizerIntent extras;
 - `detected_language`, `language_detection_confidence_level`
 and `top_locale_alternatives` key entries
 for the SpeechRecognizer result Bundle;
 - Language detection confidence levels valued
 as `UNKNOWN`, `NOT_CONFIDENT`, `CONFIDENT` and `HIGHLY_CONFIDENT`.

The following entities are created for the language switch feature:
 - `android.speech.extra.ENABLE_LANGUAGE_SWITCH`
 and `android.speech.extra.LANGUAGE_SWITCH_ALLOWED_LANGUAGES`
 key entries for the RecognizerIntent extras;
 - Language switch sensitivity levels valued
 as `high_precision`, `balanced`, and `quick_response`.
 - `language_switch_result` key entry
 for the SpeechRecognizer result Bundle;
 - Language switch results valued
 as `NOT_ATTEMPTED`, `SUCCEEDED`, `FAILED` and `SKIPPED_NO_MODEL`.

Bug: 268317656
Bug: 268475583
Test: CTS
Change-Id: I52266b1676535812c9f036149bf3a46f2aaf2340