Add tests for namespace/using related refactorings (cevelop)

[moberhuber]

The namespace/using related refactorings from the "Refactorings" section on https://www.cevelop.com/features/ look interesting and useful. It would be good adding some tests for these, perhaps at the point when results for cevelop are added.

[LegalizeAdulthood]

Add test cases for:

• Inline Using: replace unqualified identifier with fully qualified identifier and remove corresponding using declaration or using directive
• Extract Using Declaration: replace fully-qualified identifier with unqualified identifier and adds a using declaration in the local scope
• Qualify Name: replace an unqualified identifier with a fully qualified identifier