Make createTransformToString a standalone function

src/ol/has.js

@@ -45,6 +45,20 @@ export const DEVICE_PIXEL_RATIO = (function() {
   }
 })();
 
+/**
+ * The execution context is a window.
+ * @const
+ * @type {boolean}
+ */
+export const WINDOW = (function() {
+  try {
+    return 'document' in self;
+  } catch (e) {
+    // ancient browsers don't have `self`
+    return true;
+  }
+})();
+
 /**
  * Image.prototype.decode() is supported.
  * @type {boolean}