ref-count SdrObject

ref-count SdrObject

Which means we can get rid of the majestic hack of ScCaptionPtr
Previously, SdrObject was manually managed, and the ownership
passed around in very complicated fashion.

Notes:

(*) SvxShape has a strong reference to SdrObject, where
previously it had a weak reference. It is now strong
since otherwise the SdrObject will go away very eagerly.

(*) SdrObject still has a weak reference to SvxShape

(*) In the existing places that an SdrObject is being
deleted, we now just clear the reference

(*) instead of SwVirtFlyDrawObj removing itself from the
page that contains inside it's destructor, make the call site
do the removing from the page.

(*) Needed to take the SolarMutex in UndoManagerHelper_Impl::impl_clear
because this can be called from UNO (e.g. sfx2_complex JUnit test)
and the SdrObjects need the SolarMutex when destructing.

(*) handle a tricky situation with SwDrawVirtObj in the SwDrawModel
destructor because the existing code wants mpDrawObj in
SwAnchoredObject to be sometimes owning, sometimes not, which
results in a cycle with the new code.

Change-Id: I4d79df1660e386388e5d51030653755bca02a163
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/138837
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>