Add a way to get the native hardware integration buffer for a suface

When running on wayland-egl it will be a EGLImageKHR. The compositor
can then use it to pass it to something like a hardware compositor,
or a parent compositor using the egl extension
EGL_WL_create_wayland_buffer_from_image.

Change-Id: I61a165c9af444509f28ab92d00be146e2e78eb52
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>

src/compositor/compositor_api/qwaylandbufferref.cpp

@@ -126,6 +126,11 @@ void QWaylandBufferRef::destroyTexture()
         d->buffer->destroyTexture();
     }
 }
+
+void *QWaylandBufferRef::nativeBuffer() const
+{
+    return d->buffer->handle();
+}
 #endif
 
 QT_END_NAMESPACE

src/compositor/compositor_api/qwaylandbufferref.h

@@ -77,6 +77,7 @@ public:
      */
     GLuint createTexture();
     void destroyTexture();
+    void *nativeBuffer() const;
 #endif
 
 private: