Qt namespace: add a Qt 7 note about enumerator order

LayoutDirectionAuto is the default in qguiapplication.cpp's
layout_direction. Because the numeric value isn't zero, it forces the
variable into the DATA segment instead of the more efficient BSS one.

At a less technical level, LayoutDirection{} should really produce the
default, Auto, instead of LeftToRight. APIs have been changed for
lesser violations of inclusivity :)

Change-Id: I06b42f0bc00ea539805280ef0aa9694e6d739f41
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/global/qnamespace.h

@@ -1460,6 +1460,7 @@ namespace Qt {
     enum LayoutDirection {
         LeftToRight,
         RightToLeft,
+        // ### Qt 7: make auto the first one (with value 0)
         LayoutDirectionAuto
     };