Improve database queries for v2025.3

[matthew-white]

In v2025.3, we're changing a number of database queries with an eye to performance. This issue exists to keep track of what's changed so far / anything we plan to change. (I'll probably link to this issue from release notes.)

• Return less data from the database if Backend doesn't actually need that data
  • Submissions.newVersion(): reduce repeated data central-backend#1606
  • Submissions.createNew(): return less data central-backend#1608
  • Entities.createVersion(): reduce repeated data central-backend#1615
• datasets: sort results in code central-backend#1540
• Entities.createNew(): don't rewrite all related entity_defs central-backend#1614

[matthew-white]

I'm going to go ahead and mark this issue as done, since we're arcing toward regression testing. If there are more improvements made to database queries, they can be added to the list above.