Fix build of BAML decompiler.

ICSharpCode.Decompiler/Util/CollectionExtensions.cs

@@ -4,7 +4,7 @@ using System.Linq;
 
 namespace ICSharpCode.Decompiler.Util
 {
-	public static class CollectionExtensions
+	static class CollectionExtensions
 	{
 		public static void Deconstruct<K, V>(this KeyValuePair<K, V> pair, out K key, out V value)
 		{

ILSpy/ExtensionMethods.cs

@@ -159,5 +159,19 @@ namespace ICSharpCode.ILSpy
 				return s;
 			return s.Substring(0, length) + "...";
 		}
+
+		/// <summary>
+		/// Equivalent to <code>collection.Select(func).ToArray()</code>, but more efficient as it makes
+		/// use of the input collection's known size.
+		/// </summary>
+		public static U[] SelectArray<T, U>(this ICollection<T> collection, Func<T, U> func)
+		{
+			U[] result = new U[collection.Count];
+			int index = 0;
+			foreach (var element in collection) {
+				result[index++] = func(element);
+			}
+			return result;
+		}
 	}
 }