How to use the @angular/language-service/src/utils.flatten function in @angular/language-service

createElementCssSelector(element) :
                createElementCssSelector(new compiler_1.Element(elementName, [], [], null, null, null));
            var matcher = new compiler_1.SelectorMatcher();
            matcher.addSelectables(selectors);
            matcher.match(elementSelector, function (selector) {
                var directive = selectorMap.get(selector);
                if (directive) {
                    attrs_1.push.apply(attrs_1, tslib_1.__spread(Object.keys(directive.inputs).map(function (name) { return ({ name: name, input: true }); })));
                    attrs_1.push.apply(attrs_1, tslib_1.__spread(Object.keys(directive.outputs).map(function (name) { return ({ name: name, output: true }); })));
                }
            });
            // If a name shows up twice, fold it into a single value.
            attrs_1 = foldAttrs(attrs_1);
            // Now expand them back out to ensure that input/output shows up as well as input and
            // output.
            attributes.push.apply(attributes, tslib_1.__spread(utils_1.flatten(attrs_1.map(expandedAttr))));
        }
        return attributes;
    }
    function attributeValueCompletions(info, position, attr) {

// Add html properties
        var htmlProperties = html_info_1.propertyNames(elementName);
        if (htmlProperties) {
            attributes.push.apply(attributes, tslib_1.__spread(htmlProperties.map(function (name) { return ({ name: name, input: true }); })));
        }
        // Add html events
        var htmlEvents = html_info_1.eventNames(elementName);
        if (htmlEvents) {
            attributes.push.apply(attributes, tslib_1.__spread(htmlEvents.map(function (name) { return ({ name: name, output: true }); })));
        }
        var _a = utils_1.getSelectors(info), selectors = _a.selectors, selectorMap = _a.map;
        if (selectors && selectors.length) {
            // All the attributes that are selectable should be shown.
            var applicableSelectors = selectors.filter(function (selector) { return !selector.element || selector.element == elementName; });
            var selectorAndAttributeNames = applicableSelectors.map(function (selector) { return ({ selector: selector, attrs: selector.attrs.filter(function (a) { return !!a; }) }); });
            var attrs_1 = utils_1.flatten(selectorAndAttributeNames.map(function (selectorAndAttr) {
                var directive = selectorMap.get(selectorAndAttr.selector);
                var result = selectorAndAttr.attrs.map(function (name) { return ({ name: name, input: name in directive.inputs, output: name in directive.outputs }); });
                return result;
            }));
            // Add template attribute if a directive contains a template reference
            selectorAndAttributeNames.forEach(function (selectorAndAttr) {
                var selector = selectorAndAttr.selector;
                var directive = selectorMap.get(selector);
                if (directive && utils_1.hasTemplateReference(directive.type) && selector.attrs.length &&
                    selector.attrs[0]) {
                    attrs_1.push({ name: selector.attrs[0], template: true });
                }
            });
            // All input and output properties of the matching directives should be added.
            var elementSelector = element ?
                createElementCssSelector(element) :