Use media::AudioManager::GetGlobalAppName for MPRIS integration

With the fix for QTBUG-85363, the proper application name is now shown in Pulseaudio. However, Chromium's MPRIS integration still seems to hardcode the application name as Chrome/Chromium:

#if BUILDFLAG(GOOGLE_CHROME_BRANDING)
  set_property("Identity", DbusString("Chrome"));
#else
  set_property("Identity", DbusString("Chromium"));
#endif

Given that it's related to audio as well, I suppose this could use media::AudioManager::GetGlobalAppName instead of hardcoding the name as well? Not sure if a patch for that should be in QtWebEngine or Chromium upstream, though?