indev: add get_inactive_time

lv_core/lv_indev.h

@@ -94,6 +94,13 @@ bool lv_indev_is_dragging(lv_indev_t * indev);
  */
 void lv_indev_get_vect(lv_indev_t * indev, lv_point_t * point);
 
+/**
+ * Get elapsed time since last press
+ * @param indev pointer to an input device
+ * @return Elapsed ticks (milliseconds) since last press
+ */
+uint32_t lv_indev_get_inactive_time(lv_indev_t * indev);
+
 /**
  * Do nothing until the next release
  * @param indev pointer to an input device