produce column copies up the whole hierarchy first

produce column copies up the whole hierarchy first

Fixed issue where a hierarchy of classes set up as an abstract or mixin
declarative classes could not declare standalone columns on a superclass
that would then be copied correctly to a :class:`_orm.declared_attr`
callable that wanted to make use of them on a descendant class.

Originally it looked like this would produce an ordering change,
however an adjustment to the flow for produce_column_copies
has avoided that for now.

Fixes: #8190
Change-Id: I4e2ee74edb110793eb42691c3e4a0e0535fba7e9