macOS: Prevent leaking font data when creating QRawFont from QByteArrays

CTFontCreateWithGraphicsFont has a bug causing it to never release the
graphics font, which cascades down to the data provider never being
released and releaseFontData never being called.

Instead of relying on a callback to release the byte array font data,
we attach the font data to the engine's lifetime. Note that we are
still leaking the CoreFoundation types.

Change-Id: I6eda4212638ccc9439b90e004222272d204c707a
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>