AccessibilityServiceInfo does not convert correctly feedback type to string.

1. When the feedback type is set to TYPES_ALL_MASK the method
   feedbackTypeToString was not generating a string with all
   feedback types. Also the generated string sometimes could
   have a comma appended after the last feedback type name
   - this happens if the feedback type contains unknown type
   flag.

Change-Id: I848c520cf7dae16dcd882f68275869c7ab656dd7