Define getCoordinates and setCoordinates in the base class

Since these methods are implemented by all subclasses, it makes sense to
define them in the base class as abstract method.

src/ol/geom/simplegeometry.js

@@ -98,6 +98,12 @@ ol.geom.SimpleGeometry.prototype.computeExtent = function(extent) {
 };
 
 
+/**
+ * @return {Array} Coordinates.
+ */
+ol.geom.SimpleGeometry.prototype.getCoordinates = goog.abstractMethod;
+
+
 /**
  * Return the first coordinate of the geometry.
  * @return {ol.Coordinate} First coordinate.
@@ -209,6 +215,13 @@ ol.geom.SimpleGeometry.prototype.setFlatCoordinatesInternal =
 };
 
 
+/**
+ * @param {Array} coordinates Coordinates.
+ * @param {ol.geom.GeometryLayout=} opt_layout Layout.
+ */
+ol.geom.SimpleGeometry.prototype.setCoordinates = goog.abstractMethod;
+
+
 /**
  * @param {ol.geom.GeometryLayout|undefined} layout Layout.
  * @param {Array} coordinates Coordinates.