libweston: Migrate functions that operate on 'weston_spring'

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>

libweston/libweston-internal.h

@@ -263,4 +263,15 @@ weston_surface_to_buffer_region(struct weston_surface *surface,
 				pixman_region32_t *buffer_region);
 void
 weston_surface_schedule_repaint(struct weston_surface *surface);
+
+/* weston_spring */
+
+void
+weston_spring_init(struct weston_spring *spring,
+		   double k, double current, double target);
+int
+weston_spring_done(struct weston_spring *spring);
+
+void
+weston_spring_update(struct weston_spring *spring, const struct timespec *time);
 #endif

libweston/zoom.c

@@ -31,6 +31,7 @@
 #include <stdbool.h>
 
 #include <libweston/libweston.h>
+#include "libweston-internal.h"
 #include "text-cursor-position-server-protocol.h"
 #include "shared/helpers.h"