Add type annotation to EventEmitter

[FrederikBolding]

Explanation

Adds a type annotation for the EventEmitter in AbstractMessageMessenger.

Without this, TypeScript would infer EventEmitter to be generic and break types in packages consuming this package.

    hub: EventEmitter<[never]>;

Following this change, the EventEmitter is no longer inferred as generic.

    hub: EventEmitter;

Changelog

@metamask/message-manager

• Fixed: Fix EventEmitter inferred type

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've highlighted breaking changes using the "BREAKING" category above as appropriate