Fix dynamic properties in QQmlPropertyMap not always being visible in QML

QQmlPropertyMap is a fully dynamic class that can add properties at any point
in time. In order for these properties to be visible inside QML, we must
disable the property cache (instead of trying to unsuccessfully re-fresh it).

What happened in this particular case is that the QQmlPropertyMap derived type
was instantiated and the VME instruction for creating it would also assign the
property cache the compiler determined. There's no way for QQmlPropertyMap
itself to access this property cache instance (stored in
output->types[id].typePropertyCache) or invalidate it, so instead don't use the
compiler's property cache when instantiating the type.

This patch also disallows the adding properties to QQmlPropertyMap when it
is used as base type for a new QML type, as we cannot provide the derived
type to the QQmlPropertyMap constructor - this is only possible in C++.

Task-number: QTBUG-35233
Change-Id: I7fa9e4a2224ccfdd7ccb3fd9f73919ecd46058a8
Reviewed-by: Alberto Mardegan <mardy@users.sourceforge.net>
Reviewed-by: Alan Alpert (Personal) <416365416c@gmail.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Fix data layout of Managed class

The internal class should really be the first member. The
flags should go away over time.

Change-Id: Id2373a438e2af63a55704819c9dd5569c3895080
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>