Giving the map a getFeatureInfoForPixel method

This method is an entry point for getting feature information.
Renderers can use a hit canvas or defer to a layer (source) to
get matching features for a pixel.

For now this is only implemented for vector layers, and it uses
a bbox query because we cannot refine the result because of
missing geometry intersection functions yet.

src/ol/map.exports

@@ -2,6 +2,7 @@
 @exportProperty ol.Map.prototype.addLayer
 @exportProperty ol.Map.prototype.addPreRenderFunction
 @exportProperty ol.Map.prototype.addPreRenderFunctions
+@exportProperty ol.Map.prototype.getFeatureInfoForPixel
 @exportProperty ol.Map.prototype.getInteractions
 @exportProperty ol.Map.prototype.getRenderer
 @exportProperty ol.Map.prototype.removeLayer