It may be more efficient and convenient for application to use this
signal instead of metaDataChanged().
metaDataChanged() signal is emitted for compatibility,
backends should emit both signals.
Signal added QMetadataReader/WritterControl,
QMediaObject and QMediaRecorder.
Change-Id: I5ca34a40e64b22034e6fde8cd7f9735cc3f72c68
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>