Ecto 3.12: Add Query.ByExpr structs next to the old Query.QueryExpr struct matching

[sriedel]

Addresses #197

To get mongodb_ecto working with ecto 3.12 I've done the naive thing and added Ecto.Query.ByExpr structs next to the places where Ecto.Query.QueryExpr was present.

After the manually updating ecto to 3.12.5, the existing unit tests are working.

However I would need guidance on how to properly set up the tests to work with both struct types, or how to not throw an error when using with an older ecto version that does not define this struct. Nor do I have any knowledge on how matrix testing works in elixir, so pointers on where the configuration would need to be updated would be appreciated as well :).

[mweidner037]

Thanks @sriedel ! This looks reasonable to me in comparison to the ecto_sql analog (elixir-ecto/ecto_sql#607). Though I'm not sure why we cannot replace ByExpr with QueryExpr entirely (without your duplicate cases, the tests indeed fail).

Since ByExpr was added in Ecto 3.12, we need to bump our dependency on Ecto, and consumers will need to upgrade in sync. It is the same situation as ecto_sql.