Add them to BaseAccessorHolder (like `Base Category` accessors) instead of
Base class so they can be regenerated on reset while not having to remove
ZODB Components from Base class on reset.

This means that providesIFoo() will only be available on Portal Type classes
whereas before it was working for direct Document instanciation, but the latter
has been banned for several years anyway and the few remaining ones have been
fixed (23b2b5fd, e791d08a).

Also, instead of Base.provides() being a CachingMethod() (does not work with
resets), create a method dynamically on the Portal Type class (erp5.portal_type.Foo),
as not caching at all is ~18 times slower.