Investigate removing Microsoft.Extensions.* assemblies from the VSIX

[donnie-msft]

I removed Microsoft.Extensions.DependencyInjection.* assemblies from the VSIX in NuGet/NuGet.Client#7007, but it may be possible to remove these as well:

• Microsoft.Extensions.FileProviders.Abstractions.dll
• Microsoft.Extensions.FileSystemGlobbing.dll
• Microsoft.Extensions.Primitives.dll

MSBuild already has Microsoft.Extensions.Primitives.dll in its bin folder, so that one should be good.
See what actually uses the other assemblies and remove them from the VSIX if appropriate.