How to use the @angular/language-service/src/expressions.getExpressionSymbol function in @angular/language-service

visitBoundText: function (ast) {
                    var expressionPosition = templatePosition - ast.sourceSpan.start.offset;
                    if (utils_1.inSpan(expressionPosition, ast.value.span)) {
                        var dinfo = utils_1.diagnosticInfoFromTemplateInfo(info);
                        var scope = language_services_1.getExpressionScope(dinfo, path, /* includeEvent */ false);
                        var result = expressions_1.getExpressionSymbol(scope, ast.value, expressionPosition, info.template.query);
                        if (result) {
                            symbol_1 = result.symbol;
                            span_1 = utils_1.offsetSpan(result.span, ast.sourceSpan.start.offset);
                        }
                    }
                },
                visitText: function (ast) { },

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);
                            }
                        }
                        return true;
                    }
                }
                return false;
            };
            path.tail.visit({