[1.x] Add custom JSON serializer

[kapi2289]

Resolves #21. @Naamloos, please let me know if this implementation solves your issue.

You can use a custom JSON serializer in your app by creating a custom class implementing the IInertiaSerializer
interface:

using System.Text.Json;
using System.Text.Json.Serialization;
using Microsoft.AspNetCore.Mvc;

public class CustomSerializer : IInertiaSerializer
{
    // Used in HTML responses
    public string Serialize(object? obj)
    {
        // Default serialization
        return JsonSerializer.Serialize(obj, new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
            ReferenceHandler = ReferenceHandler.IgnoreCycles
        });
    }

    // Used in JSON responses
    public JsonResult SerializeResult(object? obj)
    {
        // Default serialization
        return new JsonResult(obj, new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
            ReferenceHandler = ReferenceHandler.IgnoreCycles
        });
    }
}

or extending the DefaultInertiaSerializer class, which also implements the IInertiaSerializer interface:

public class CustomSerializer : DefaultInertiaSerializer
{
    protected new static JsonSerializerOptions GetOptions()
    {
        // Default options
        return new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
            ReferenceHandler = ReferenceHandler.IgnoreCycles
        };
    }
}

You can then register it in the configuration:

builder.Services.AddInertia();

[...]

builder.Services.UseInertiaSerializer<CustomSerializer>();

[...]

app.UseInertia();