Add initial pass of write support, always write out ol.style.Stroke as LineSymbolizer

src/ol/style/textsymbolizer.js

@@ -215,6 +215,15 @@ ol.style.Text.prototype.getZIndex = function() {
 };
 
 
+/**
+ * Get the stroke.
+ * @return {ol.style.Stroke} Stroke.
+ */
+ol.style.Text.prototype.getStroke = function() {
+  return this.stroke_;
+};
+
+
 /**
  * Set the font color.
  * @param {ol.expr.Expression} color Font color.