Replace Newtonsoft.Json package with System.Text.Json

[NCLnclNCL]

We use Newtonsoft.Json package to serialize/deserialize json. It is great library. But seems json is becoming built-in format in BCL (.net 6). In future it allow us to be not dependent on any 3rd-party libraries. We will produce multi-targeted package:

netstandard2.0 - depends on System.Text.Json net6.0 - has no dependencies Newtonsoft.Json dont support native aot but System.Text.Json support with source generator