Make NoActiveSeletion_Throws() test virtual

Passing a null IDeclarationFinderProvider reference may cause some
subclasses to fail or throw an unexpected Exception prior to generating
the expected Exception.  Support overriding when needed (e.g.,
EncapsulateFieldRefactoring tests)

Author: BZngr

RubberduckTests/Refactoring/RefactoringTestBase.cs

@@ -21,7 +21,7 @@ public abstract class RefactoringTestBase
     {
         [Test]
         [Category("Refactorings")]
-        public void NoActiveSelection_Throws()
+        public virtual void NoActiveSelection_Throws()
         {
             var rewritingManager = new Mock<IRewritingManager>().Object;
             var refactoring = TestRefactoring(rewritingManager, null, initialSelection: null);