This method was composing a frame that was only accurate for devices
with a pixelRatio of 1. Now the canvas widths and heights are
multiplied beforehand by the pixelRatio. #5601
The update has been added to the docs for all 'forEachLayerAtPixel' definitions
and currently returns null for non-supporting definitions. ol.Color typeDef
was also updated to support Uint8Arrays & Uint8ClampedArrays as it is the
reference type for the addded argument #5586
Benjamin