Add missing WMSGetFeatureInfo exports

The idea when adding `getFeatureInfoOptions` to `ol.source.TileWMSSource` and `ol.source.ImageWMSSource` was to provide an easy way to configure the method and additional parameters that should be used for GetFeatureInfo. As it turns out, this does not work in the built version because `objectliterals.jsdoc` needs the property name on the first line of the property definition.