Add Dictionary<TKey, TValue>

Tests/GenericCollections/GenericCollections.nfproj

@@ -27,6 +27,7 @@
   <Import Project="$(NanoFrameworkProjectSystemPath)NFProjectSystem.props" Condition="Exists('$(NanoFrameworkProjectSystemPath)NFProjectSystem.props')" />
   <ItemGroup>
     <Compile Include="CollectionTestBase.cs" />
+    <Compile Include="DictionaryTests.cs" />
     <Compile Include="ListTests.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
   </ItemGroup>

nanoFramework.System.Collections/Collections/Generic/DebugViewDictionaryItem.cs

@@ -0,0 +1,32 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics;
+
+namespace System.Collections.Generic
+{
+    /// <summary>
+    /// Defines a key/value pair for displaying an item of a dictionary by a debugger.
+    /// </summary>
+    [DebuggerDisplay("{Value}", Name = "[{Key}]")]
+    internal readonly struct DebugViewDictionaryItem<TKey, TValue>
+    {
+        public DebugViewDictionaryItem(TKey key, TValue value)
+        {
+            Key = key;
+            Value = value;
+        }
+
+        public DebugViewDictionaryItem(KeyValuePair<TKey, TValue> keyValue)
+        {
+            Key = keyValue.Key;
+            Value = keyValue.Value;
+        }
+
+        [DebuggerBrowsable(DebuggerBrowsableState.Collapsed)]
+        public TKey Key { get; }
+
+        [DebuggerBrowsable(DebuggerBrowsableState.Collapsed)]
+        public TValue Value { get; }
+    }
+}