Add System.Text.Json support

[Kim-SSi]

Change the strings containing tabs to use \t. Add System.Text.Json support Add new settings:

Use System.Text.Json instead of Newtonsoft.Json public bool UseSystemTextJson { get; set; }

Generated data types will be decorated with JsonProperty with the PropertyName in C#. public bool DecorateDataModelWithPropertyName { get; set; }

Disable property nullable by default. Set by the OpenApi v3 option nullable public bool DisableSystemNullableByDefault { get; set; }

Use T? instead of System.Nullable. C# 8.0 feature public bool UseCSharpNullable { get; set; }

Create the Model classes only public bool GenerateModelsOnly { get; set; }

Create arrays as List public bool ArrayAsList { get; set; }

Create arrays as ICollection public bool ArrayAsICollection { get; set; }