Add new active effect type that can modify an item's details, rather than actor

[arbron]

Core to the enchantment system (#3305) is a new active effect type (specified by flag for now, using a proper active effect type in V12) that allows the active effect changes to apply to the item rather than to the containing actor.

• This effect would never be transferred to the actor or offered up in the current effect application UI
• Dropping this active effect onto an item works, but dropping it onto an actor throws an error
• Would be skipped during the normal actor active effect application
• Would be applied during new item active effect application
• Only works for physical items

See also: https://github.com/foundryvtt/foundryvtt/issues/10185