Allow migration of charges to an equivalent amount of single items

[mqrause]

Summary

Infrastructure "Allow migration of charges to an equivalent amount of single items"

Purpose of change

Fixes #54376

Describe the solution

Put charges - 1 items of the same itype in the migration pocket of the item.
Migration pocket handling isn't ideal since it only unloads items on the player and not on the map and always drops stuff to the ground instead of (trying to) put it in the location the main item is in.

Describe alternatives you've considered

Doing it by default for all items that shouldn't be count_by_charges and aren't on the charge removal blacklist, but that might lead to unexpected results. That can still be done later when it's relevant.

Testing

Tested migrating the itype leather by changing its type to GENERIC and adding it to the list.

Additional context

Sorry for stealing this from the person who was working on it, but I got annoyed by items with charges and this is an important step to remove that.

[Maleclypse]

The hero GitHub deserves.