desktop-shell: make get_output_work_area() global

get_output_work_area() can be used by exposay to know the free space
where it can render its surfaces, what avoids overlapping the panel.

Currently this function is declared as static in
desktop-shell/shell.c, so it cannot be used by exposay.

Remove static from get_output_work_area() and add it to shell.h
so it can be used by exposay as well.

Signed-off-by: Leandro Ribeiro <leandrohr@riseup.net>

desktop-shell/shell.c

@@ -334,7 +334,7 @@ get_output_panel_size(struct desktop_shell *shell,
 	/* the correct view wasn't found */
 }
 
-static void
+void
 get_output_work_area(struct desktop_shell *shell,
 		     struct weston_output *output,
 		     pixman_rectangle32_t *area)

desktop-shell/shell.h

@@ -235,6 +235,11 @@ get_shell_surface(struct weston_surface *surface);
 struct workspace *
 get_current_workspace(struct desktop_shell *shell);
 
+void
+get_output_work_area(struct desktop_shell *shell,
+		     struct weston_output *output,
+		     pixman_rectangle32_t *area);
+
 void
 lower_fullscreen_layer(struct desktop_shell *shell,
 		       struct weston_output *lowering_output);