Mono Fix for Unsafe Mode (#4887)

* Added preprocessor define for C++ if Template Aliases are supported by the compiler

* Revert "Revert "Performance Increase of Vector of Structures using .NET BlockCopy (#4830)""

This reverts commit 1f5eae5d6a.

* Put<T> method was inside #if UNSAFE_BYTEBUFFER which caused compilation failure when building in unsafe mode

* Revert "Added preprocessor define for C++ if Template Aliases are supported by the compiler"

This reverts commit a75af73521.

net/FlatBuffers/FlatBufferBuilder.cs

@@ -179,6 +179,18 @@ namespace FlatBuffers
             _bb.PutFloat(_space -= sizeof(float), x);
         }
 
+        /// <summary>
+        /// Puts an array of type T into this builder at the 
+        /// current offset
+        /// </summary>
+        /// <typeparam name="T">The type of the input data </typeparam>
+        /// <param name="x">The array to copy data from</param>
+        public void Put<T>(T[] x)
+            where T : struct
+        {
+            _space = _bb.Put(_space, x);
+        }
+
         public void PutDouble(double x)
         {
             _bb.PutDouble(_space -= sizeof(double), x);
@@ -245,6 +257,37 @@ namespace FlatBuffers
         /// <param name="x">The `float` to add to the buffer.</param>
         public void AddFloat(float x) { Prep(sizeof(float), 0); PutFloat(x); }
 
+        /// <summary>
+        /// Add an array of type T to the buffer (aligns the data and grows if necessary).
+        /// </summary>
+        /// <typeparam name="T">The type of the input data</typeparam>
+        /// <param name="x">The array to copy data from</param>
+        public void Add<T>(T[] x)
+            where T : struct
+        {
+            if (x == null)
+            {
+                throw new ArgumentNullException("Cannot add a null array");
+            }
+
+            if( x.Length == 0)
+            {
+                // don't do anything if the array is empty
+                return;
+            }
+
+            if(!ByteBuffer.IsSupportedType<T>())
+            {
+                throw new ArgumentException("Cannot add this Type array to the builder");
+            }
+
+            int size = ByteBuffer.SizeOf<T>();
+            // Need to prep on size (for data alignment) and then we pass the
+            // rest of the length (minus 1) as additional bytes
+            Prep(size, size * (x.Length - 1));
+            Put(x);
+        }
+
         /// <summary>
         /// Add a `double` to the buffer (aligns the data and grows if necessary).
         /// </summary>