missing x-objc++src mimetype

I notice that Qt includes a private copy of the shared-mime-info database (freedesktop.org.xml) for use on platforms that do not typically have s-m-i installed. That includes the Mac platform, for which a not negligible number of Qt's own source files are written in ObjC++.

I think it'd be good if the bundled freedesktop.org.xml had an entry for that language (i.e. x-objc+src with extension .mm and inheriting x-c+src as well as x-objsrc).