consider propagate_to_loaders at application time

consider propagate_to_loaders at application time

Fixed regression from 1.4 where using :func:`_orm.defaultload` in
conjunction with a non-propagating loader like :func:`_orm.contains_eager`
would nonetheless propagate the :func:`_orm.contains_eager` to a lazy load
operation, causing incorrect queries as this option is only intended to
come from an original load.

Fixes: #11292
Change-Id: I79928afa108970b523f2166c3190f7952eca73ed
(cherry picked from commit 80399cefa1b16a8548ba0c997a1eda94b8e9db01)