Problem/Motivation
- Back when MenuLink was an entity type, #1966298: Introduce menu link bundles per menus introduced bundles for it, where the bundle is the menu that the link is in (just like taxonomy terms have a bundle corresponding to the vocabulary they're in). This was to allow different link translation settings per menu.
- #2301317: MenuLinkNG part4: Conversion changed MenuLink from an entity type to a plugin type, and plugins have no concept of bundles. It added a new entity type, MenuLinkContent, specifically for custom menu links, but made them have just a single bundle, not bundle = menu.
- MenuLinkContent is now a fieldable entity type (by default), whereas the old MenuLink wasn't. Meanwhile, a link can be moved from one menu to another, and core's Field API does not have support for changing the bundle of a fieldable entity.
Proposed resolution
Discuss and figure out what our options are.