function tryHandleExtension(root, field) {
    var extendedType = field.parent.lookup(field.extend);
    if (extendedType) {
        var sisterField = new Field(field.fullName, field.id, field.type, field.rule, undefined, field.options);
        sisterField.declaringField = field;
        field.extensionField = sisterField;
        extendedType.add(sisterField);
        return true;
    }
    return false;
}
Handles a deferred declaring extension field by creating a sister field to represent it within its extended type.
@param {Root} root Root instance
@param {Field} field Declaring extension field witin the declaring type
@returns {boolean} `true` if successfully added to the extended type, `false` otherwise
@inner
@ignore