Improve toJson() method implementation to prevent from System.OutOfMemoryException for large number of records

[mparvanov]

Description

Improve the toJson() method current implementation which uses Newtonsoft.Json internally to prevent from System.OutOfMemoryException for large number of records

Reproduction of the problem

Create an action method that returns JSON from an excel document with large number of records:

public ActionResult Read()
        {
            var cuastomerPath = Server.MapPath("~/App_Data/AR_Converter.xlsx");
            var workbook = Telerik.Web.Spreadsheet.Workbook.Load(cuastomerPath);

            //Uses Newtonsoft.Json internally to serialize fields correctly.
            return Content(workbook.ToJson(), Telerik.Web.Spreadsheet.MimeTypes.JSON);
        }

Current behavior

Exception of type 'System.OutOfMemoryException' was thrown.

Expected/desired behavior

No errors are thrown

Environment

• Kendo UI version: 2018.1.221