Inconsistent FlaggingEvent and UnflaggingEvent parameters make hard to reuse same code to handl

Problem/Motivation

As a module developer that wants to take advantage of flag module and implement my own logic of some updates based on flagged/unflagged content, I'd like to subscribe to both events at the same time, and I have no problems with that, but every time one will subscribe to both events, they will have to handle events differently in their code, as the API is inconsistent, FlaggingEvent works with one flagging, while UnflaggingEvent works with an array of flaggings.

Proposed resolution

Drupal core content entities use foreach to iterate over entities in postDelete and send hook_entity_delete separately for every one, I'm wondering if it would be better for DX to do the same for UnflaggingEvent.

Remaining tasks

Provide a patch

User interface changes

None

API changes

UnflaggingEvent constructor accepts array of flaggings entities, after the change it should accept one flagging.

Data model changes

None