Subquery deconstruction support required implementing complex and
expensive equality rules for sql.Query objects for little benefit as
the latter cannot themselves be made deconstructible to their reference
to model classes.
Making Expression @deconstructible and not BaseExpression allows
interested parties to conform to the "expression" API even if they are
not deconstructible as it's only a requirement for expressions allowed
in Model fields and meta options (e.g. constraints, indexes).
Thanks Phillip Cutter for the report.
This also fixes a performance regression in bbf141bcdc31f1324048af9233583a523ac54c94.
By making Query subclass BaseExpression in
35431298226165986ad07e91f9d3aca721ff38ec the former defined it's
identity based off _construct_args which is not appropriate.
This prevent having to pass simple_col through multiple function calls
by defining whether or not references should be resolved with aliases
at the Query level.