dont assume ClauseElement in attributes, coercions

dont assume ClauseElement in attributes, coercions

Fixed two distinct issues, each of which would come into play under certain
circumstances, most likely however one which is a common mis-configuration
in :class:`_hybrid.hybrid_property`, where the "expression" implementation
would return a non :class:`_sql.ClauseElement` such as a boolean value.
For both issues, 1.3's behavior was to silently ignore the
mis-configuration and ultimately attempt to interpret the value as a
SQL expression, which would lead to an incorrect query.

* Fixed issue regarding interaction of the attribute system with
hybrid_property, where if the ``__clause_element__()`` method of the
attribute returned a non-:class:`_sql.ClauseElement` object, an internal
``AttributeError`` would lead the attribute to return the ``expression``
function on the hybrid_property itself, as the attribute error was
against the name ``.expression`` which would invoke the ``__getattr__()``
method as a fallback. This now raises explicitly. In 1.3 the
non-:class:`_sql.ClauseElement` was returned directly.

* Fixed issue in SQL argument coercions system where passing the wrong
kind of object to methods that expect column expressions would fail if
the object were altogether not a SQLAlchemy object, such as a Python
function, in cases where the object were not just coerced into a bound
value. Again 1.3 did not have a comprehensive argument coercion system
so this case would also pass silently.

Fixes: #6350
Change-Id: I5bba0a6b27f45e5f8ebadfd6d511fa773388ef7c