Support undocumented non-entity sequence Query argument

Support undocumented non-entity sequence Query argument

Fixed regression caused by :ticket:`4256` (itself a regression fix for
:ticket:`4228`) which breaks an undocumented behavior which converted for a
non-sequence of entities passed directly to the :class:`.Query` constructor
into a single-element sequence.  While this behavior was never supported or
documented, it's already in use so has been added as a behavioral contract
to :class:`.Query`.

Change-Id: I97546f5ab5af29f37c86321f39d564f98a12daf5
Fixes: #4269