Optimize ImmutableSortedSet<T>.SetEquals to avoid unnecessary allocations

Author: Ahmed

src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet_1.cs

@@ -375,24 +375,52 @@ public bool SetEquals(IEnumerable<T> other)
                 return true;
             }
 
+            if (other is ImmutableSortedSet<T> immutableSortedSet && immutableSortedSet.KeyComparer == this.KeyComparer)
+            {
+                if (immutableSortedSet.Count != this.Count)
+                {
+                    return false;
+                }
+                foreach (T item in immutableSortedSet)
+                {
+                    if (!this.Contains(item))
+                    {
+                        return false;
+                    }
+                }
+
+                return true;
+            }
+
+            else if (other is SortedSet<T> sortedSet && sortedSet.Comparer == this.KeyComparer)
+            {
+                if (sortedSet.Count != this.Count)
+                {
+                    return false;
+                }
+                foreach (T item in sortedSet)
+                {
+                    if (!this.Contains(item))
+                    {
+                        return false;
+                    }
+                }
+                return true;
+            }
+
             var otherSet = new SortedSet<T>(other, this.KeyComparer);
-            if (this.Count != otherSet.Count)
+            if (otherSet.Count != this.Count)
             {
                 return false;
             }
-
-            int matches = 0;
             foreach (T item in otherSet)
             {
                 if (!this.Contains(item))
                 {
                     return false;
                 }
-
-                matches++;
             }
-
-            return matches == this.Count;
+            return true;
         }
 
         /// <summary>