examples: fix build on macOS with gtk+-quartz-3.0

gdk_quartz_window_get_nsview is not declared in the header file now:
error: implicit declaration of function 'gdk_quartz_window_get_nsview'
is invalid in C99 [-Werror,-Wimplicit-function-declaration]

fixes #979

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2116>

subprojects/gst-docs/examples/tutorials/basic-tutorial-5.c

@@ -11,6 +11,10 @@
 #include <gdk/gdkwin32.h>
 #elif defined (GDK_WINDOWING_QUARTZ)
 #include <gdk/gdkquartz.h>
+#if GTK_CHECK_VERSION(3, 24, 10)
+#include <AppKit/AppKit.h>
+NSView *gdk_quartz_window_get_nsview (GdkWindow * window);
+#endif
 #endif
 
 /* Structure to contain all our information, so we can pass it around */

subprojects/gst-examples/playback/player/gtk/gtk-play.c

@@ -33,6 +33,10 @@
 #include <gdk/gdkwin32.h>
 #elif defined (GDK_WINDOWING_QUARTZ)
 #include <gdk/gdkquartz.h>
+#if GTK_CHECK_VERSION(3, 24, 10)
+#include <AppKit/AppKit.h>
+NSView *gdk_quartz_window_get_nsview (GdkWindow * window);
+#endif
 #endif
 
 #include <gtk/gtk.h>

subprojects/gst-plugins-base/tests/examples/gl/gtk/gstgtk.c

@@ -35,6 +35,10 @@
 #endif
 #if GST_GL_HAVE_WINDOW_COCOA && defined(GDK_WINDOWING_QUARTZ)
 #include <gdk/gdkquartz.h>
+#if GTK_CHECK_VERSION(3, 24, 10)
+#include <AppKit/AppKit.h>
+NSView *gdk_quartz_window_get_nsview (GdkWindow * window);
+#endif
 #endif
 
 gboolean

subprojects/gst-plugins-base/tests/examples/playback/playback-test.c

@@ -41,6 +41,10 @@
 #include <gdk/gdkwin32.h>
 #elif defined (GDK_WINDOWING_QUARTZ)
 #include <gdk/gdkquartz.h>
+#if GTK_CHECK_VERSION(3, 24, 10)
+#include <AppKit/AppKit.h>
+NSView *gdk_quartz_window_get_nsview (GdkWindow * window);
+#endif
 #endif
 
 #include <gst/video/videooverlay.h>