Update ChatApps to use MagicOnion v6 Structure

[guitarrapc]

tl;dr;

• Remain ChatApp .NET Framework (.NET Framework 462), but can be work with .NET Standard 2.1, too.
• ChatApp.Shared to reference MessagePack.Annotations, instead of MessagePack.
• Use NuGetForUnity to install Dependency dlls, instead of direct dll install.
• Packages updates.
  • Install NuGetForUnity via git UPM.
  • Use Latest YetAnotherHttpHandlerr 1.2.0

Note

MessagePack installation notice

If you use NuGetForUnity to install MessagePack, you can't reference MessagePack.Unity.UnityResolver.Instance because NuGet's MessagePack doesn't include this.
To resolve this issue, use MessagePack's .unitypackage.

ChatApp

Works fine with Unity 2021.3.0f1