Add API for Designer to QLayout

• Make qSmartMinSize accessible
• We want a factory method hook for those places in which the QWidgetItems/QSpacerItems are created (by the layout) and and we need to invoke that method.
  Currently, in 4.4, this is:

class QLayoutPrivate {
typedef QWidgetItem * (*QWidgetItemFactoryMethod)(const QLayout *layout, QWidget *widget);
typedef QSpacerItem * (*QSpacerItemFactoryMethod)(const QLayout *layout, int w, int h, QSizePolicy::Policy hPolicy, QSizePolicy::Policy);
static QWidgetItem *createWidgetItem(const QLayout *layout, QWidget *widget);
static QSpacerItem *createSpacerItem(const QLayout *layout, int w, int h, QSizePolicy::Policy hPolicy = QSizePolicy::Minimum, QSizePolicy::Policy vPolicy = QSizePolicy::Minimum);
static QWidgetItemFactoryMethod widgetItemFactoryMethod;
static QSpacerItemFactoryMethod spacerItemFactoryMethod;

To make this very flexible, we could
enum QtHook

static SomeCentralClass::setHook(int enumValue, void *);
static void *SomeCentralClass::hook(int enumValue);
providing method ptrs can be reinterpret_casted to void* everywhere?

• Potentially: Have a different default font size for embedded?

Please look at the parent task as to why this makes sense.
As of 8.2.2008, Designer will not be the LSB test app; still we would like to
get rid of _p.h