Add new Mosa.Utility.CreateCoreLib tool

[AnErrupTion]

Hello! This PR adds a new tool to MOSA's arsenal, called Mosa.Utility.CreateCoreLib. Its purpose is to create a "stub" core library project, i.e. a core library with the exact same API surface as the official core library, but with none of its implementations. I've updated the documentation to add this new tool as well. Documentation will come in a later PR.

I've also made the following changes to accodomate for this new tool, and the future new project based on it:

• Updated the C# language version to 12.0
• Re-organized the linked documentation files in both solutions

[tgiphil]

LGTM - Just rename project with Mosa.Utility preix.