Resolve "Tidy-up batchable preloading"

What does this MR do and why?

This MR simplifies the way we manage preloading of dependencies in BoardListType#title, to reduce the encoding of low-level details.

This could (eventually) be generalized to a helper for GraphQL object methods if it proves to be of wider applicability.

How to set up and validate locally

This should have no observable effect.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #342889 (closed)