Bypass declared_attr w/ a custom wrapper for lambda criteria

Bypass declared_attr w/ a custom wrapper for lambda criteria

Fixed bug in new :func:`_orm.with_loader_criteria` feature where using a
mixin class with :func:`_orm.declared_attr` on an attribute that were
accessed inside the custom lambda would emit a warning regarding using an
unmapped declared attr, when the lambda callable were first initialized.
This warning is now prevented using special instrumentation for this
lambda initialization step.

Fixes: #6320
Change-Id: I18ce0c662131f2e683b84caa38c01b2182eb210b