Add support for custom comparer for NodeCollection and set altertative comparer for oracle

Oracle RDBMS supports case-sensitive schemas so schemas collection has to support
case-sensitive name index.

Author: alex-kulakov

Orm/Xtensive.Orm/Sql/Model/Catalog.cs

@@ -198,10 +198,20 @@ internal string GetActualDbName(IDictionary<string, string> catalogNameMap)
 
     // Constructors
 
-    public Catalog(string name) : base(name)
+    public Catalog(string name)
+      : base(name)
     {
       schemas =
         new PairedNodeCollection<Catalog, Schema>(this, "Schemas", 1);
     }
+
+    public Catalog(string name, bool caseSensitiveNames = false)
+      : base(name)
+    {
+      schemas = caseSensitiveNames
+        ? new PairedNodeCollection<Catalog, Schema>(this, "Schemas", 1, StringComparer.Ordinal)
+        : new PairedNodeCollection<Catalog, Schema>(this, "Schemas", 1, StringComparer.OrdinalIgnoreCase);
+    }
+
   }
 }

Orm/Xtensive.Orm/Sql/Model/NodeCollection.cs

@@ -84,5 +84,16 @@ public NodeCollection(int capacity)
     {
       nameIndex = new Dictionary<string, TNode>(capacity, Comparer);
     }
+
+    /// <summary>
+    /// Initializes new instance of this type.
+    /// </summary>
+    /// <param name="capacity">The initial collection capacity.</param>
+    /// <param name="comparer">Comparer for inner name index.</param>
+    public NodeCollection(int capacity, IEqualityComparer<string> comparer)
+      : base(capacity)
+    {
+      nameIndex = new Dictionary<string, TNode>(capacity, comparer);
+    }
   }
 }

Orm/Xtensive.Orm/Sql/Model/PairedNodeCollection.cs

@@ -4,6 +4,7 @@
 
 using System;
 using System.Collections;
+using System.Collections.Generic;
 using Xtensive.Core;
 
 namespace Xtensive.Sql.Model
@@ -73,6 +74,24 @@ public PairedNodeCollection(TOwner owner, string property, int capacity)
       this.property = property;
     }
 
+    /// <summary>
+    /// Initializes a new instance of the <see cref="PairedNodeCollection{TOwner,TNode}"/> class.
+    /// </summary>
+    /// <param name="owner">The collection owner.</param>
+    /// <param name="property">Owner collection property.</param>
+    /// <param name="capacity">The initial collection capacity.</param>
+    /// <param name="equalityComparer">Comparer for inner name index.</param>
+    public PairedNodeCollection(TOwner owner, string property, int capacity, IEqualityComparer<string> equalityComparer)
+      : base(capacity, equalityComparer)
+    {
+      ArgumentValidator.EnsureArgumentNotNull(owner, nameof(owner));
+      ArgumentValidator.EnsureArgumentNotNullOrEmpty(property, nameof(property));
+      ArgumentValidator.EnsureArgumentNotNull(equalityComparer, nameof(equalityComparer));
+
+      this.owner = owner;
+      this.property = property;
+    }
+
     #endregion
   }
 }