Add string comparison of tones

[wangrui-msft]

Description

Add conversion to string from a collection of tones.

        RecognizeCompleted recognizeCompletedEvent = (RecognizeCompleted) event;
        Optional<RecognizeResult> dtmfResult = recognizeCompletedEvent.getRecognizeResult();
        CollectTonesResult tonesResult = (CollectTonesResult) dtmfResult.get();

        String tones = tonesResult.convertToString();
        if (tones.equals("1234567") {
        // do something
        }

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[azure-sdk]

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azure-communication-callautomation