function setMessageProperty(msg,prop,value,createMissing) {
    if (prop.indexOf('msg.')===0) {
        prop = prop.substring(4);
    }
    return setObjectProperty(msg,prop,value,createMissing);
}
Sets a property of a message object.

Unlike {@link @node-red/util-util.setObjectProperty}, this function will strip `msg.` from the
front of the property expression if present.

@param  {Object}  msg           - the message object
@param  {String}  prop          - the property expression
@param  {any}     value         - the value to set
@param  {boolean} createMissing - whether to create missing parent properties
@memberof @node-red/util_util