Custom Assets wont create if not registered in the `AssemblyRegistry`

Release Type: Official Release

Version: 4.2.0.2293

Platform(s): Windows

Describe the bug
When following the Custom Assets manual the Add asset option is there but upon clicking it the asset never gets created.

To Reproduce
Steps to reproduce the behavior:

1. follow https://doc.stride3d.net/latest/en/manual/scripts/custom-assets.html
2. put the templates and asset code in a separate external project
3. see that the asset is shown in the Add Asset window
4. Try adding the asset and see it does not get added

Expected behavior
The asset should be created.

Additional context
This is more for people to find a common issue if they are following a similar project structure of have multiple projects.
I will update the docs when I can and complete https://github.com/stride3d/stride-docs/issues/390 to show that its done.

Current Fix
Just create a class called Module.cs in the external project with the asset files and add the below code with your namespace:

using System.Reflection;
using Stride.Core;
using Stride.Core.Reflection;

YOUR_NAMESPACE;

internal class Module
{
    [ModuleInitializer]
    public static void Initialize()
    {
        // "AssemblyCommonCategories.Assets" gets registered on startup of the project in GameStudio and allows the template to be created from a separate project.
        AssemblyRegistry.Register(typeof(Module).GetTypeInfo().Assembly, AssemblyCommonCategories.Assets);
    }
}

Reproduce the issue by following the Custom Assets manual with templates and asset code in an external project. Start with the external project's Module.cs example and the AssemblyRegistry.Register entry point, then verify that the asset shown in the Add Asset window is created successfully; the related documentation update is tracked in stride-docs issue 390.