PropertyContainer uses a static member of type PropertyData to register
static properties. PropertyData uses a short variable to record the
offset of the property against its container.
Because of possible 'short' truncation, when searching of property that
in fact is from another container, we must check if the pointer within
boundary. Otherwise, truncation will result in effectively random
number, and possibly causing a false hit.
I'm still finding typos in the source code. I propose that you keep this PR open prior ro relaese and then merge so that if I find other typos in the meantime they will be part this release.
Due to problems onthe windows platform the virtual inheritance approach must be dropped. NExt to the already reimplemented proeprty interface the Type interface is reimplemented too. This change allows to revert some earlier changes.
FreeCADs property system utilises some pointer math to calculate the offset between
property and base class. Due to virtual inheritance of th ePropertyContainer the memory
layout has been changed to rather random, which has lead to crashes dependend on the
order of object initialisation.
The solution is to not make PropertyContaner virtual but a class below, Base::Persitance.
Then the memory layout is random for Persistance, but it is perfectly aligned for the
base class chains from PropertyContainer onwards as well as from Extension onwards.
Hence the proeprty system was changed to take the offset always from those two.
