Return a Heap object from the getter()/setter() methods of Property

We actually need to put the returned value into a ScopedFunctionObject
before calling it, as the Property could get deleted during the call
leading to a dangling pointer. With a GC that moves objects this will
become even more important.

Change-Id: I43bece6f80eb3501c1291065846e230a59ae8aed
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Use Scoped values a bit more consistently

Mainly cleanups, but also one or two potential places that could
lead to issues with a moving GC.

Change-Id: Ia388420052cd1a642120773f582bf21965830613
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Use pointers to Heap object to avoid recursion

Change-Id: If491b35ba43758bd4792166f7213cd5a11d227d9
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Store a pointer to a heap object in the context wrapper

Change-Id: I2555e3e78e429260129d83894ca94d158c5e1704
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Store a heap object in the qmlextensions

Change-Id: I5ad9236378ff1e037945d024ee5bd6629dddec4d
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Make Property uses GC safe

Change-Id: I5aa41a07a2d25e5c8a2d64bfa58a55fcd7aaf77e
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>