Use tuples in more cases.

src/Workspaces/Core/Portable/Shared/Collections/IntervalTree`1.cs

@@ -113,16 +113,16 @@ private IEnumerable<T> GetInOrderIntervals(int start, int length, TestInterval t
             var end = start + length;
 
             // The bool indicates if this is the first time we are seeing the node.
-            var candidates = new Stack<ValueTuple<Node, bool>>();
-            candidates.Push(ValueTuple.Create(root, true));
+            var candidates = new Stack<(Node node, bool firstTime)>();
+            candidates.Push((root, true));
 
             while (candidates.Count > 0)
             {
                 var currentTuple = candidates.Pop();
-                var currentNode = currentTuple.Item1;
+                var currentNode = currentTuple.node;
                 Debug.Assert(currentNode != null);
 
-                var firstTime = currentTuple.Item2;
+                var firstTime = currentTuple.firstTime;
 
                 if (!firstTime)
                 {
@@ -148,18 +148,18 @@ private IEnumerable<T> GetInOrderIntervals(int start, int length, TestInterval t
                         var right = currentNode.Right;
                         if (right != null && GetEnd(right.MaxEndNode.Value, introspector) >= start)
                         {
-                            candidates.Push(ValueTuple.Create(right, true));
+                            candidates.Push((right, firstTime: true));
                         }
                     }
 
-                    candidates.Push(ValueTuple.Create(currentNode, false));
+                    candidates.Push((currentNode, firstTime: false));
 
                     // only if left's maxVal overlaps with interval's start, we should consider 
                     // left subtree
                     var left = currentNode.Left;
                     if (left != null && GetEnd(left.MaxEndNode.Value, introspector) >= start)
                     {
-                        candidates.Push(ValueTuple.Create(left, true));
+                        candidates.Push((left, firstTime: true));
                     }
                 }
             }
@@ -243,22 +243,22 @@ public IEnumerator<T> GetEnumerator()
             }
 
             // The bool indicates if this is the first time we are seeing the node.
-            var candidates = new Stack<ValueTuple<Node, bool>>();
+            var candidates = new Stack<(Node node, bool firstTime)>();
             candidates.Push(ValueTuple.Create(root, true));
             while (candidates.Count != 0)
             {
                 var currentTuple = candidates.Pop();
-                var currentNode = currentTuple.Item1;
+                var currentNode = currentTuple.node;
                 if (currentNode != null)
                 {
-                    if (currentTuple.Item2)
+                    if (currentTuple.firstTime)
                     {
                         // First time seeing this node.  Mark that we've been seen and recurse
                         // down the left side.  The next time we see this node we'll yield it
                         // out.
-                        candidates.Push(ValueTuple.Create(currentNode.Right, true));
-                        candidates.Push(ValueTuple.Create(currentNode, false));
-                        candidates.Push(ValueTuple.Create(currentNode.Left, true));
+                        candidates.Push((currentNode.Right, firstTime: true));
+                        candidates.Push((currentNode, firstTime: false));
+                        candidates.Push((currentNode.Left, firstTime: true));
                     }
                     else
                     {