QMenu: Enable sloppy submenu mouse navigation

Since we're in the 21st century, we set QCommonStyle to return true
to the SH_Menu_SloppySubMenus style hint. This unlocks all the logic
already available in QMenu.

Task-number: QTBUG-20094
[ChangeLog][QtWidgets][QMenu] Enable sloppy submenu mouse navigation
Change-Id: I134c87e348d98d1f46055e0bfef2b4a4a3d2993a
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

src/widgets/styles/qcommonstyle.cpp

@@ -4896,6 +4896,10 @@ int QCommonStyle::styleHint(StyleHint sh, const QStyleOption *opt, const QWidget
         ret = 256;
         break;
 
+    case SH_Menu_SloppySubMenus:
+        ret = true;
+        break;
+
     case SH_ProgressDialog_TextLabelAlignment:
         ret = Qt::AlignCenter;
         break;

src/widgets/styles/qmacstyle_mac.mm

@@ -2532,9 +2532,6 @@ int QMacStyle::styleHint(StyleHint sh, const QStyleOption *opt, const QWidget *w
         ret = QDialogButtons::Reject;
         break;
         */
-    case SH_Menu_SloppySubMenus:
-        ret = true;
-        break;
     case SH_GroupBox_TextLabelVerticalAlignment:
         ret = Qt::AlignTop;
         break;

src/widgets/styles/qstyle.cpp

@@ -1706,8 +1706,10 @@ void QStyle::drawItemPixmap(QPainter *painter, const QRect &rect, int alignment,
 
     \value SH_Menu_Scrollable Whether popup menus must support scrolling.
 
-    \value SH_Menu_SloppySubMenus Whether popupmenu's must support
-        sloppy submenu; as implemented on Mac OS.
+    \value SH_Menu_SloppySubMenus  Whether popup menus must support
+        the user moving the mouse cursor to a submenu while crossing
+        other items of the menu. This is supported on most modern
+        desktop platforms.
 
     \value SH_ScrollView_FrameOnlyAroundContents  Whether scrollviews
         draw their frame only around contents (like Motif), or around