Add typed fast paths in ReadArray for common element types

Avoid Array.CreateInstance + Array.SetValue reflection overhead
for object[], string[], and Type[] arrays in metadata deserialization.

Author: davkean

src/Microsoft.VisualStudio.Composition/Configuration/SerializationContextBase.cs

@@ -756,6 +756,41 @@ protected Array ReadArray(BinaryReader reader, Func<object?> itemReader, Type el
                     throw new NotSupportedException();
                 }
 
+                // Use typed fast paths for common element types to avoid
+                // the overhead of Array.CreateInstance + Array.SetValue (reflection + boxing).
+                if (elementType == typeof(object))
+                {
+                    var array = new object?[(int)count];
+                    for (int i = 0; i < array.Length; i++)
+                    {
+                        array[i] = itemReader();
+                    }
+
+                    return array;
+                }
+
+                if (elementType == typeof(string))
+                {
+                    var array = new string?[(int)count];
+                    for (int i = 0; i < array.Length; i++)
+                    {
+                        array[i] = (string?)itemReader();
+                    }
+
+                    return array;
+                }
+
+                if (elementType == typeof(Type))
+                {
+                    var array = new Type?[(int)count];
+                    for (int i = 0; i < array.Length; i++)
+                    {
+                        array[i] = (Type?)itemReader();
+                    }
+
+                    return array;
+                }
+
                 var list = Array.CreateInstance(elementType, (int)count);
                 for (int i = 0; i < list.Length; i++)
                 {