Rename frame_create and frame_set_child_size with a window_ prefix

This is to avoid a collision with an actual frame structure.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
diff --git a/clients/nested.c b/clients/nested.c
index 5085234..ff59014 100644
--- a/clients/nested.c
+++ b/clients/nested.c
@@ -583,7 +583,7 @@
 		return nested;
 
 	nested->window = window_create(display);
-	nested->widget = frame_create(nested->window, nested);
+	nested->widget = window_frame_create(nested->window, nested);
 	window_set_title(nested->window, "Wayland Nested");
 	nested->display = display;