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/PathUtil.cpp

@@ -42,7 +42,7 @@ namespace Path
         // Directory named filenames containing ":" are invalid, so we can assume if there is a :
         // it will be the drive name.
         pchCurrentPosition = strchr(pchLastPosition, ':');
-        if (pchCurrentPosition == NULL)
+        if (pchCurrentPosition == nullptr)
         {
             rstrDriveLetter = "";
         }
@@ -54,7 +54,7 @@ namespace Path
 
         pchCurrentPosition = strrchr(pchLastPosition, '\\');
         pchAuxPosition = strrchr(pchLastPosition, '/');
-        if ((pchCurrentPosition == NULL) && (pchAuxPosition == NULL))
+        if ((pchCurrentPosition == nullptr) && (pchAuxPosition == nullptr))
         {
             rstrDirectory = "";
         }
@@ -70,7 +70,7 @@ namespace Path
         }
 
         pchCurrentPosition = strrchr(pchLastPosition, '.');
-        if (pchCurrentPosition == NULL)
+        if (pchCurrentPosition == nullptr)
         {
             rstrExtension = "";
             strFilename.assign(pchLastPosition);
@@ -114,7 +114,7 @@ namespace Path
         do
         {
             pchCurrentPosition = strpbrk(pchLastPosition, "\\/");
-            if (pchCurrentPosition == NULL)
+            if (pchCurrentPosition == nullptr)
             {
                 break;
             }