Editor code: tidy up BOOLs,NULLs and overrides pt4.

A few 'typedefs' replaced by 'using's
This shouldn't have any functional changes at all, just c++17 modernization
It's a part 4 of a split #2847

Signed-off-by: Nemerle <nemerle5+git@gmail.com>

Code/Editor/Util/DynamicArray2D.cpp

@@ -58,7 +58,7 @@ CDynamicArray2D::~CDynamicArray2D()
     }
 
     delete [] m_Array;
-    m_Array = 0;
+    m_Array = nullptr;
 }