REST endpoint for …/entities does not use a stable order

[matthew-white]

Problem description

The OData feed for entities returns entities in a stable order, with the most recently created entity coming first:

https://github.com/getodk/central-backend/blob/983ec81e69793fdb589ffdc346a16ef977489be4/lib/model/query/entities.js#L452

However, the REST endpoint for …/entities returns entities in a different order, with the entity that was created or updated least recently coming first (essentially). Note that because the order is sensitive to updates, it isn't stable.

https://github.com/getodk/central-backend/blob/983ec81e69793fdb589ffdc346a16ef977489be4/lib/model/query/entities.js#L372

Steps to reproduce the problem

1. Create an entity with a label of "foo". Create a second entity with a label of "bar".
2. Observe that initially, …/entities lists foo before bar.
3. Update foo.
4. Observe that now, …/entities lists bar before foo.

Expected behavior

I think that the OData feed for submissions and the REST endpoint for …/submissions return submissions in the same order. Maybe entity endpoints should likewise be consistent?