moving apidiff out of preview (#3595)

release-notes/3.0/api-diff/.Net/3.0.0_System.Text.Json.Serialization.md

@@ -0,0 +1,45 @@
+# System.Text.Json.Serialization
+
+``` diff
++namespace System.Text.Json.Serialization {
++    public abstract class JsonAttribute : Attribute {
++        protected JsonAttribute();
++    }
++    public abstract class JsonConverter {
++        public abstract bool CanConvert(Type typeToConvert);
++    }
++    public abstract class JsonConverter<T> : JsonConverter {
++        protected internal JsonConverter();
++        public override bool CanConvert(Type typeToConvert);
++        public abstract T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options);
++        public abstract void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options);
++    }
++    public class JsonConverterAttribute : JsonAttribute {
++        protected JsonConverterAttribute();
++        public JsonConverterAttribute(Type converterType);
++        public Type ConverterType { get; }
++        public virtual JsonConverter CreateConverter(Type typeToConvert);
++    }
++    public abstract class JsonConverterFactory : JsonConverter {
++        protected JsonConverterFactory();
++        public abstract JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options);
++    }
++    public sealed class JsonExtensionDataAttribute : JsonAttribute {
++        public JsonExtensionDataAttribute();
++    }
++    public sealed class JsonIgnoreAttribute : JsonAttribute {
++        public JsonIgnoreAttribute();
++    }
++    public sealed class JsonPropertyNameAttribute : JsonAttribute {
++        public JsonPropertyNameAttribute(string name);
++        public string Name { get; }
++    }
++    public sealed class JsonStringEnumConverter : JsonConverterFactory {
++        public JsonStringEnumConverter();
++        public JsonStringEnumConverter(JsonNamingPolicy namingPolicy = null, bool allowIntegerValues = true);
++        public override bool CanConvert(Type typeToConvert);
++        public override JsonConverter CreateConverter(Type typeToConvert, JsonSerializerOptions options);
++    }
++}
+```
+