API to provide context for SFSpeechRecognizer with a context phrase

FB20692995 If SFSpeechRecognizer is used to detect a specific kind of phrase, like a location name, it boosts recognition rates if the user says "city dodoma" instead of just "dodoma", especially for location names that are not that common and can be confused with other words. This might also apply to other phrase types like person names, ingredients, etc. API suggestion: Add a property to pre-warm SFSpeechRecognizer with a short context phrase that clarifies the context.