function setEPSGLookup(func) {
  epsgLookup = func;
}
Set the lookup function for getting proj4 definitions given an EPSG code.
By default, the {@link module:ol/proj/proj4.fromEPSGCode} function uses the
epsg.io website for proj4 definitions.  This can be changed by providing a
different lookup function.

@param {function(number):Promise<string>} func The lookup function.
@api