There were historical reasons (namely the SUL unification) why the rename request process was in the CentralAuth extension, but I think these days it'd be better if it was in an independent extension and was usable with both GlobalRename and the normal renameuser in core.

Plan

• Pick a name for the new extension
• Copy-paste code from CentralAuth to the new extension to get it barely working
• Update CentralAuth to not register its special pages if new extension is enabled
• Get new extension deployed to beta
• Get new extension deployed to production
• Remove old code from CentralAuth
• Gradually make new extension less CentralAuth specific