Initial scaffolding for CLI introspection

[Flash0ver]

Summary

Add projects for CLI introspection, both ".NET SDK CLI Schema" and the "OpenCLI Specification".

Remarks

• Library projects to pack NuGet packages from
  • mark Trimmable and AOT-compatible
• Sample/Demo projects for C#, F#, and Visual Basic
  • also to test consumption/usage in these .NET languages
• Testing project
  • use MSTest.Sdk
• Benchmarking project
  • use BenchmarkDotNet

See also

• Add CLI Schema Option for System.CommandLine #3
• Add OpenCLI Specification Option for System.CommandLine #4