[CWEP002] Add schema finalization checks for computed attributes
``finalize_computed_attributes`` essentially checks that computed attributes
types match with the type declaration of the attribute.
Related to #3546717.
[CWEP002] Account for attribute formula in schema bootstrap
This isn't enough to have computed attribute support, it is only in order not to
crash when yams 0.40 is used.
Related to #3546717.