APIView: `protected internal` members rendered in .NET APIViews as `protected`

We have some `protected internal` APIs in the .NET Core libraries that are being rendered as `protected` today. It would be nice to render these as `protected internal` as it helps communicate the need for them and how they are used.

Start with the .NET APIViews rendering path and trace how protected internal members are classified and displayed. Check the existing APIViews tests if available, then verify that these members render as “protected internal” while other access levels remain unchanged.

Written by the indexing model from the issue text.