GraphQL4 - resolve async write using System.Text.Json

[MikeKry]

Replace newtonsoft.json with System.Text.Json to allow async write directly to response

handles - buffered stream issue from (#10782)

[MikeKry]

I have resolved problem reported by @sebastienros in #9087

Info about newtonsoft vs system.text.json here: https://graphql-dotnet.github.io/docs/guides/serialization/

In case of updating to GraphQL5,

request = await JsonSerializer.DeserializeAsync<GraphQLRequest>(context.Request.Body, new JsonSerializerOptions { WriteIndented = false, PropertyNamingPolicy = JsonNamingPolicy.CamelCase });

and

_.Inputs = request.Variables.ToInputs();

can be replaced by IGraphQLSerializer

 var request = await _serializer.ReadAsync<GraphQLRequest>(context.Request.Body, context.RequestAborted);

Tested both post and get api.

[sebastienros]

I like it