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

function interpolationCompletions(info, position) {
        // Look for an interpolation in at the position.
        var templatePath = utils_1.findTemplateAstAt(info.templateAst, position);
        var mostSpecific = templatePath.tail;
        if (mostSpecific) {
            var visitor = new ExpressionVisitor(info, position, undefined, function () { return language_services_1.getExpressionScope(utils_1.diagnosticInfoFromTemplateInfo(info), templatePath, false); });
            mostSpecific.visit(visitor, null);
            return utils_1.uniqueByName(visitor.result);
        }
    }
    // There is a special case of HTML where text that contains a unclosed tag is treated as

function attributeValueCompletions(info, position, attr) {
        var path = utils_1.findTemplateAstAt(info.templateAst, position);
        var mostSpecific = path.tail;
        var dinfo = utils_1.diagnosticInfoFromTemplateInfo(info);
        if (mostSpecific) {
            var visitor = new ExpressionVisitor(info, position, attr, function () { return language_services_1.getExpressionScope(dinfo, path, false); });
            mostSpecific.visit(visitor, null);
            if (!visitor.result || !visitor.result.length) {
                // Try allwoing widening the path
                var widerPath_1 = utils_1.findTemplateAstAt(info.templateAst, position, /* allowWidening */ true);
                if (widerPath_1.tail) {
                    var widerVisitor = new ExpressionVisitor(info, position, attr, function () { return language_services_1.getExpressionScope(dinfo, widerPath_1, false); });
                    widerPath_1.tail.visit(widerVisitor, null);
                    return widerVisitor.result;
                }
            }
            return visitor.result;
        }
    }
    function elementCompletions(info, path) {

function attributeValueCompletions(info, position, attr) {
        var path = utils_1.findTemplateAstAt(info.templateAst, position);
        var mostSpecific = path.tail;
        var dinfo = utils_1.diagnosticInfoFromTemplateInfo(info);
        if (mostSpecific) {
            var visitor = new ExpressionVisitor(info, position, attr, function () { return language_services_1.getExpressionScope(dinfo, path, false); });
            mostSpecific.visit(visitor, null);
            if (!visitor.result || !visitor.result.length) {
                // Try allwoing widening the path
                var widerPath_1 = utils_1.findTemplateAstAt(info.templateAst, position, /* allowWidening */ true);
                if (widerPath_1.tail) {
                    var widerVisitor = new ExpressionVisitor(info, position, attr, function () { return language_services_1.getExpressionScope(dinfo, widerPath_1, false); });
                    widerPath_1.tail.visit(widerVisitor, null);
                    return widerVisitor.result;
                }
            }
            return visitor.result;
        }

function locateSymbol(info) {
        if (!info.position)
            return undefined;
        var templatePosition = info.position - info.template.span.start;
        var path = utils_1.findTemplateAstAt(info.templateAst, templatePosition);
        if (path.tail) {
            var symbol_1 = undefined;
            var span_1 = undefined;
            var attributeValueSymbol_1 = function (ast, inEvent) {
                if (inEvent === void 0) { inEvent = false; }
                var attribute = findAttribute(info);
                if (attribute) {
                    if (utils_1.inSpan(templatePosition, utils_1.spanOf(attribute.valueSpan))) {
                        var dinfo = utils_1.diagnosticInfoFromTemplateInfo(info);
                        var scope = language_services_1.getExpressionScope(dinfo, path, inEvent);
                        if (attribute.valueSpan) {
                            var expressionOffset = attribute.valueSpan.start.offset + 1;
                            var result = expressions_1.getExpressionSymbol(scope, ast, templatePosition - expressionOffset, info.template.query);
                            if (result) {
                                symbol_1 = result.symbol;
                                span_1 = utils_1.offsetSpan(result.span, expressionOffset);