eglTerminate kills Qt window on wayland when sharing the same display between interface and vout_window

This is a tracking issue for the following discussions:

• https://mailman.videolan.org/pipermail/vlc-devel/2019-September/127761.html

• https://mailman.videolan.org/pipermail/vlc-devel/2019-October/127953.html

Currently, the only way to do video embedding between the UI and the vout_window in wayland is to share the wl_display between both. When using a vout with EGL provider, it will use the same EGLDisplay between the vout and the interface. When calling eglTerminate then, it will kill both EGLDisplay.

One solution is using refcounting through EGL_KHR_display_reference, but it's not supported everywhere, and especially not on open source MESA drivers.

It's a blocking issue for video integration in Qt interface