Update build, analyzers to match core Autofac

[tillig]

• Change build to GitHub Actions. This means new Autofac.Extensions.DependencyInjection packages will be published in GitHub Packages rather than on MyGet.
• Switch to use the central .github folder for the organization instead of one-off versions in the repo.
• Update analyzer rules to match core Autofac.
• Fix analyzer issues due to new rules.

[tillig]

Unclear how to remove the AppVeyor check here without fully closing and creating a new PR, so I'm going to do that.