[FEAT] Add New Reaction Event

[TyrantKingBen]

Problem Description

There is no handling for when a message has all reactions of a specific emoji removed. An event would be useful here for when reactions are being used to maintain some sort of state.

Proposed Solution

Add a raw_message_reaction_remove_emoji processor to the ReactionEvents event mixin. Create a MessageReactionRemoveEmoji event that extends the MessageReactionRemoveAll event and adds a PartialEmoji attribute.

Alternatives Considered

No response

Additional Information

No response

Code of Conduct

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