When referencing .NETStandard 2.0 assemblies coming from NuGet package like System.Text.Json (https://www.nuget.org/packages/System.Text.Json/5.0.2) we are getting the following error in the Editor (before this, we need to disable validation for assemblies, as there is another set of validation errors separated from this issue)

```
Error: Could not load signature of System.HexConverter:ToBytesBuffer due to: Could not load file or assembly 'System.Memory, Version=4.0.1.1, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51' or one of its dependencies.
Unloading broken assembly Assets/Scenes/System.Text.Json.dll, this assembly can cause crashes in the runtime
```

The problem is that this System.Text.Json assembly comes only in .NETStandard 2.0 form but has dependencies to:

NuGet Packages:
- Microsoft.Bcl.AsyncInterfaces (>= 5.0.0)
- System.Text.Encodings.Web (>= 5.0.1)

Special NuGet Packages but when running in a .NET runtime supporting .NET Standard 2.1, these assemblies are included with the runtime:
- System.Buffers (>= 4.5.1)
- System.Memory (>= 4.5.4)
- System.Runtime.CompilerServices.Unsafe (>= 5.0.0)
- System.Numerics.Vectors (>= 4.5.0)
- System.Threading.Tasks.Extensions (>= 4.5.4)

So it seems that the editor doesn't have the special assemblies above (System.Buffers/System.Memory) in the runtime.
Checking further the AOT folder `Data\MonoBleedingEdge\lib\mono\unityaot-win32\Facades` and comparing it to the one used at editor time `Data\MonoBleedingEdge\lib\mono\unityjit-win32\Facades`, we can see that we are missing some of these assemblies:

- System.Buffers.dll
- System.Memory.dll
- System.Threading.Tasks.Extensions.dll

Copying these DLLs to the `unityjit-win32\Facades` folder is fixing the issue.

Reproducible with a recent 2021.2 or 2022.1

Attached a project ModernDotNet.zip that contains these assemblies to reproduce the issue.