Classes derived from IStartupLocaleSelector is marked as unused if not serialisable

This is used from Unity's new localisation package

Start by reproducing the unused-marking behavior with a class derived from IStartupLocaleSelector that is not serialisable, using Unity's new localisation package. Trace which inspection or entry point marks the class as unused; done means valid derived classes are no longer incorrectly reported as unused. The issue names no files or tests, so locating the relevant code will require repository research.

Written by the indexing model from the issue text.