Write fill and outline in PolyStyle

Write styles based on style objects appropriate for geometry.
Write fill and outline in PolyStyle if false (i.e. non-default)
Handle MultiLineString, MultiPoint and MultiPolygon within heterogenous MultiGeometry when writing features

Add getGeometriesArrayRecursive method to ol/geom/GeometryCollection to allow for nested MultiGeometry

Enhanced write GeometryCollection geometries test

A more rigorous write GeometryCollection geometries test including nested collections (the output is simplified to a single MultiGeomtry)

Add writeFeatures to outline and fill tests, setting geometry for geometry specific tests

Add <fill>0</fill> and <outline>0</outline> to some existing tests

src/ol/geom/GeometryCollection.js

@@ -126,6 +126,23 @@ class GeometryCollection extends Geometry {
     return this.geometries_;
   }
 
+  /**
+   * @return {Array<Geometry>} Geometries.
+   */
+  getGeometriesArrayRecursive() {
+    /** @type {Array<Geometry>} */
+    let geometriesArray = [];
+    const geometries = this.geometries_;
+    for (let i = 0, ii = geometries.length; i < ii; ++i) {
+      if (geometries[i].getType() === this.getType()) {
+        geometriesArray = geometriesArray.concat(/** @type {GeometryCollection} */ (geometries[i]).getGeometriesArrayRecursive());
+      } else {
+        geometriesArray.push(geometries[i]);
+      }
+    }
+    return geometriesArray;
+  }
+
   /**
    * @inheritDoc
    */