Editor code: tidy up BOOLs,NULLs and overrides pt2.

A few 'typedefs' replaced by 'using's
This shouldn't have any functional changes at all, just c++17 modernization
It's a part 2 of a split #2847

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

Code/Editor/Plugins/ProjectSettingsTool/Validators.cpp

@@ -16,7 +16,7 @@
 
 namespace 
 {
-    typedef ProjectSettingsTool::FunctorValidator::ReturnType RetType;
+    using RetType = ProjectSettingsTool::FunctorValidator::ReturnType;
 
     static const int noMaxLength = -1;
     static const int maxIosVersionLength = 18;