Move load events to a special wrap of the Load function

[AndreLouisIssa]

The sanitiser for ModData is too strict, preventing writes that should be feasible as soon as Load has finished executing.
(Since Load runs before OnPreThingCreation, itself before OnAnyLoad)

[AndreLouisIssa]

safest option (avoids breaking changes):
Update the condition ModData uses
Add a new function once_loaded.save_early
Maybe add a new function ModUtil.LoadOnceEarly (for use with Hades/Pyre)