Expose internals of game/library project to editor and unit test projects by default

[peter-r-g]

What it is?

Currently the internals of a game/library project cannot be consumed by the editor or unit test projects without the following attributes:

using System.Runtime.CompilerServices;

// Allows IDEs to compile.
[assembly: InternalsVisibleTo( "example.editor" )]
[assembly: InternalsVisibleTo( "example.unittest" )]

// Allows S&box to compile.
[assembly: InternalsVisibleTo( "package.local.example.editor" )]
[assembly: InternalsVisibleTo( "package.local.example.unittest" )]

What should it be?

The source generation should just generate these for you if they do not exist already. The editor and unit test projects are supplementary to the main project so it makes sense that they should have access to internal functionality.

[garrynewman]

I don't see any reason for this

[QuackCola]

I dunno what this would be for . Sounds similar to my issue here? #6284 unless I'm mistaking something.