This change also adds some type annotations for better type
checking, introduces different write options for writing
transactions and queries, and provides new writeGetFeature and
writeTransaction methods.
This separates the action of requesting an extent to be loaded from the action of requesting cached features. The renderer (or any other consumer of a vector source) calls load to request a data extent. A `featureload` event fires when new features are loaded. The renderer (or any other consumer) separately asks for cached features given an extent. This vector source only loads features once, but this separation will also work with sources that make multiple requests for data in different extents.
This also removes the `data` option from the vector source in favor of a `features` option. Since we no longer have shared data structures for geometries, people can manually create features and pass them to a vector source. The `addFeatures` method is exported as well. This is used to add features to a source that don't have a representation on the "remote" (or server).
This moves the feature cache from ol.layer.Vector to ol.source.Vector. These are the minimum changes required to maintain the existing functionality and make tests pass. More refactoring to come.
We need to be able to set axisOrientation on the underlying GML parser of the Filter subparser of ol.parser.WFS*, also only options and no properties on the instance anymore
The tests revealed that polygons can be drawn with counter-clockwise exterior ring order. In the polygon constructor, we enforce clockwise winding for exterior rings. So after drawing, we pass polygon coordinates back to the constructor before adding feature to the target layer.
Our geometries are mutable, so they can be modified without
creating garbage by changing coordinates in place and calling
setGeometry afterwards. But this also means that we need to
create a deep clone of the coordinates.
