Packaging from VS extension

### Describe the bug

When referencing the CommunityToolkit.Mvvm package from a Visual Studio 2022 extension, the extension fails to load due to missing files.

Here's the log from VS activity log:
`System.IO.FileNotFoundException: Could not load file or assembly 'CommunityToolkit.Mvvm, Version=8.1.0.0, Culture=neutral, PublicKeyToken=4aff67a105548ee2' or one of its dependencies`

When trying to debug this, it seems that System.Buffers aren't packaged in VSIX (nor deployed to the experimental instance).

Any thoughts on this? Thanks!

### Regression

_No response_

### Steps to reproduce

```text
Reference CommunityToolkit.Mvvm from VS extension project
```

### Expected behavior

A VS 2022 extension referencing CommunityToolkit.Mvvm should load just fine.

### Screenshots

_No response_

### IDE and version

VS 2022

### IDE version

17.5.3

### Nuget packages

- [ ] CommunityToolkit.Common
- [ ] CommunityToolkit.Diagnostics
- [ ] CommunityToolkit.HighPerformance
- [X] CommunityToolkit.Mvvm (aka MVVM Toolkit)

### Nuget package version(s)

8.1.0

### Additional context

_No response_

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