Add SequenceEqualityComparer which implements Equals and GetHashCode in a manner compatible with Java's List interface

runtime/CSharp/Antlr4.Runtime/Antlr4.Runtime.csproj

@@ -153,6 +153,7 @@
     <Compile Include="Sharpen\DictionaryExtensions.cs" />
     <Compile Include="Sharpen\ListExtensions.cs" />
     <Compile Include="Sharpen\Runtime.cs" />
+    <Compile Include="Sharpen\SequenceEqualityComparer`1.cs" />
     <Compile Include="TokenStreamRewriter.cs" />
     <Compile Include="TokenTypes.cs" />
     <Compile Include="Tree\AbstractParseTreeVisitor`1.cs" />

runtime/CSharp/Antlr4.Runtime/Sharpen/SequenceEqualityComparer`1.cs

@@ -0,0 +1,52 @@
+namespace Sharpen
+{
+    using System.Collections.Generic;
+    using System.Linq;
+
+    public class SequenceEqualityComparer<T> : EqualityComparer<IEnumerable<T>>
+    {
+        private static readonly SequenceEqualityComparer<T> _default = new SequenceEqualityComparer<T>();
+
+        private readonly IEqualityComparer<T> _elementEqualityComparer = EqualityComparer<T>.Default;
+
+        public SequenceEqualityComparer()
+            : this(null)
+        {
+        }
+
+        public SequenceEqualityComparer(IEqualityComparer<T> elementComparer)
+        {
+            _elementEqualityComparer = elementComparer ?? EqualityComparer<T>.Default;
+        }
+
+        public new static SequenceEqualityComparer<T> Default
+        {
+            get
+            {
+                return _default;
+            }
+        }
+
+        public override bool Equals(IEnumerable<T> x, IEnumerable<T> y)
+        {
+            if (x == y)
+                return true;
+            if (x == null || y == null)
+                return false;
+
+            return x.SequenceEqual(y, _elementEqualityComparer);
+        }
+
+        public override int GetHashCode(IEnumerable<T> obj)
+        {
+            if (obj == null)
+                return 0;
+
+            int hashCode = 1;
+            foreach (T element in obj)
+                hashCode = 31 * hashCode + _elementEqualityComparer.GetHashCode(element);
+
+            return hashCode;
+        }
+    }
+}