Fix ToJson and FromJson liquid files for System.Text.Json

[unchase]

Now generates:

...
public string ToJson() 
{
    return System.Text.Json.JsonSerializer.Serialize(this, new System.Text.Json.JsonSerializerOptions(); var converters = new System.Text.Json.Serialization.JsonConverter[] { new Converter1() });
}
...

---

Fixed in this PR (need to check).

[unchase]

@RicoSuter ready for review

[RicoSuter]

In the end we should clean this up as I'm not a fan to parse/split etc. code in the templates..
but for now it's probably fine. What do you think?

/cc @jeremyVignelles

[jeremyVignelles]

I might have missed something, but what's the rationale of this? why are there two instructions that you need to split?
Why should it be done there rather than in a property in the C# code?

[unchase]

@jeremyVignelles

Initially, the CSharpJsonSerializerGenerator.GenerateJsonSerializerParameterCode method was intended for the Newtonsoft.Json library and allows you to return the required code as a single line (along with initialization of custom converters).
When it became necessary to add support for System.Text.Json, there were two options, due to the fact that adding custom converters for System.Text.Json is different with Newtonsoft.Json and cannot be done in the initializer of the System.Text.Json.JsonSerializerOptions class (which allows Newtonsoft.Json.JsonSerializerSettings):

1. Add everything in one line and then split this line into two parts (as implemented now).
2. Refactor the CSharpJsonSerializerGenerator.GenerateForJsonLibrary method in such a way that backward compatibility is lost (due to the possible addition of a separate method that returns the addition of custom converters for System.Text.Json).

Thus, I chose the first option. Perhaps the issue can be solved in another way. If you have any ideas on how to do this, I would be grateful.

[jeremyVignelles]

It seems that the CSharpJsonSerializerGenerator.GenerateJsonSerializerParameterCode is used for the purpose of setting the parameters to the Deserialize and Serialize methods. Why is there a ; var converters = there ?

Refactor the CSharpJsonSerializerGenerator.GenerateForJsonLibrary method in such a way that backward compatibility is lost (due to the possible addition of a separate method that returns the addition of custom converters for System.Text.Json).

I'd be OK for breaking backward compatibility to add a new Method/Property that would be specific to STJ

That said, I don't have the whole picture and that's still quite obscure for me, but making assumption on the shape of the generated code seems really rigid to me. What if I want to override the C# code to generate the converters my own way ?

[unchase]

Need to think about how to refactor the method to make it more flexible.

[unchase]

Related: #1341