Update Orm/Xtensive.Orm/Sql/Dml/Collections/SqlColumnCollection.cs

Co-authored-by: Alexey Kulakov <alexey.kulakov@dataobjects.net>

Author: SergeiPavlov

Orm/Xtensive.Orm/Sql/Dml/Collections/SqlColumnCollection.cs

@@ -24,6 +24,9 @@ public class SqlColumnCollection : ICollection<SqlColumn>, IReadOnlyList<SqlColu
     /// </summary>
     public int Count => columnList.Count;
 
+    /// <summary>
+    /// Gets or sets capacity of the collection.
+    /// </summary>
     public int Capacity {
       get => columnList.Capacity;
       set => columnList.Capacity = value;