Add System.Text.Json Support

[salarzobir]

When targeting .NET Core 3.0 or higher using System.Text.Json will increase the performance and reduce the memory usage.
Maybe the json serializer could be like a provider that user can change it when configure Audit.NET

[thepirat000]

That would be nice to have, but will be a very hard task since the library is highly coupled with newtonsoft.json, specifically with the use of the attributes JsonExtensionData and JsonProperty to annotate all the audit event classes on most of the extensions.

So we'll need to first circunvent all the compile-time issues like this in order to provide a way to select the serialization mechanism at run-time.

Feel free to make any suggestions for this

[thepirat000]

I still think providing a mechanism to change the serialization at run-time will be very hard to accomplish.

Maybe we can just default to use system.text.json internally intead of json.net on the assemblies targeting >= .net core 3, and if it was needed, provide alternative assemblies/packages to force the non-default serializarion mechanism (i.e. Audit.NET.NewtonsoftJson)

[thepirat000]

I've started trying with System.Text.Json and in less than 5 minutes I've found two open issues that will prevent a smooth migration:

• Missing reference loop handling setting: Should we add support to ignore cycles on serialization? dotnet/runtime#40099
• Missing serialization from DOM: We should be able serialize and deserialize from DOM dotnet/runtime#31274

So I think that, at this time, System.Text.Json api is not mature enough to start the migration of this library.

[thepirat000]

8358983

[thepirat000]

Added support to System.Text.Json starting on version 18 (only for .NET >= 5.0)

Refer to the following README sections:

• Breaking change on version 18
• Global serialization mechanism

All the libraries were impacted since this was a very big change (184 files changed) so please expect some backward compatibility issues on the new serialization mechanism, even though all the unit tests and integration tests are passing, specially since the System.Text.Json doesn't support (yet?) a lot of things that Newtonsoft.Json does.

Please upgrade your references to version 18.0.0 and test.