Make compatible with Unity 2020 LTS

Author: seannowotny

Runtime/SpanExtensions.cs

@@ -55,9 +55,9 @@ public static NativeArray<T> ToNativeArray<T>(this Span<T> source, Allocator all
         public static NativeArray<T> ToNativeArray<T>(this ReadOnlySpan<T> source, Allocator allocator)
             where T : unmanaged
         {
-            NativeArray<T> newArray = new(source.Length, allocator, NativeArrayOptions.UninitializedMemory);
+            NativeArray<T> newArray = new NativeArray<T>(source.Length, allocator, NativeArrayOptions.UninitializedMemory);
             newArray.CopyFrom(source);
             return newArray;
         }
     }
-}
+}