ManhattanStyle: Fix size of field in form layouts on OS X

The default in QMacStyle, to use FieldsStayAtSizeHint, just almost
always is the wrong thing to do. Additionally this goes undetected for a
while most of the time, because most people do not run their code on OS
X. Override it globally to AllNonFixedFieldsGrow like in other shipped
styles.

Task-number: QTCREATORBUG-14337
Change-Id: I3b0719c0201871fbf0163b54b1a54823bf5d14f3
Reviewed-by: Daniel Teske <daniel.teske@theqtcompany.com>

src/plugins/coreplugin/manhattanstyle.cpp

@@ -43,6 +43,7 @@
 #include <QApplication>
 #include <QComboBox>
 #include <QDockWidget>
+#include <QFormLayout>
 #include <QLabel>
 #include <QLineEdit>
 #include <QMenuBar>
@@ -372,6 +373,11 @@ int ManhattanStyle::styleHint(StyleHint hint, const QStyleOption *option, const
             if (activationMode.isValid())
                 ret = activationMode.toBool();
         }
+    case QStyle::SH_FormLayoutFieldGrowthPolicy:
+        // The default in QMacStyle, FieldsStayAtSizeHint, is just always the wrong thing
+        // Use the same as on all other shipped styles
+        if (Utils::HostOsInfo::isMacHost())
+            ret = QFormLayout::AllNonFixedFieldsGrow;
     default:
         break;
     }