[dotnet] Make some classes in internal folder as really to be internal

[nvborisenko]

Description

Internal stuff should be internal.

Motivation and Context

Sometimes selenium's classes appears in IDE suggestions, and these classes are supposed to be for internal usage. Like PortUtilities class.. I don't think Selenium is created for networking.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[diemol]

@nvborisenko can I merge this one? (If CI passes, of course)

[nvborisenko]

Unfortunately no, CI will be failing. I don't know how to configure bazel, need help from @shs96c.