Use patterns in more places.

src/Workspaces/Core/Portable/Shared/Extensions/SemanticModelExtensions.cs

@@ -80,9 +80,9 @@ public static TSymbol GetEnclosingSymbol<TSymbol>(this SemanticModel semanticMod
                  symbol != null;
                  symbol = symbol.ContainingSymbol)
             {
-                if (symbol is TSymbol)
+                if (symbol is TSymbol tSymbol)
                 {
-                    return (TSymbol)symbol;
+                    return tSymbol;
                 }
             }
 

src/Workspaces/Core/Portable/Shared/Extensions/SyntaxNodeExtensions.cs

@@ -38,9 +38,9 @@ public static IEnumerable<TNode> GetAncestors<TNode>(this SyntaxNode node)
             var current = node.Parent;
             while (current != null)
             {
-                if (current is TNode)
+                if (current is TNode tNode)
                 {
-                    yield return (TNode)current;
+                    yield return tNode;
                 }
 
                 current = current is IStructuredTriviaSyntax