Primary support for System.Text.Json

For .NET Client API, strongly typed OpenAPI Client Generators have been well supporting Newtonsoft.Json and System.Text.Json. Since .NET 6 and ASP.NET 7, System.Text.Json has become comprehensive. The primary support of this codegen is now shifted from Newtonsoft.Json to System.Text.Json.

In this release, the features for Angular, Aurelia, AXIOS, Fetch API, and jQuery remain unchanged.