`dotnet run file.cs` `#:` directive for `ItemGroup`

[ShortDevelopment]

Is your feature request related to a problem? Please describe.

The dotnet run file.cs document list the #:property directive to include a property (PropertyGroup) but no directive to include an item (ItemGroup).

Describe the solution you'd like

• A #:item name "value" directive that generates

  <ItemGroup>
     <Name Include="value" />
  </ItemGroup>

Additional context

This would be useful to include additional files used by source-generators.
For example:

#:package Google.Protobuf 3.*
#:package Grpc.Tools 2.*

#:item Protobuf "somefile.proto"

Console.WriteLine("Do some stuff");