fix(MessageReaction): defines the client property in the type

[itsa-sh]

Please describe the changes this PR makes and why it should be merged:

I created an issue #5002 this is the PR to resolve it. I wasn't 100% sure i've followed the contribution guidelines.

This solves the missing client property from the MessageReaction typing

Status

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating

Semantic versioning classification:

• This PR changes the library's interface (methods or parameters added)
• This PR includes breaking changes (methods removed or renamed, parameters moved or removed)
• This PR only includes non-code changes, like changes to documentation, README, etc.

[NotSugden]

this should be above count, to be sorted alphabetically

[itsa-sh]

No worries, I'll update in the morning :)

[kyranet]

LGTM, the property exists in the JS code.

discord.js/src/structures/MessageReaction.js

Lines 18 to 24 in b8fd3f6

	/**
	* The client that instantiated this message reaction
	* @name MessageReaction#client
	* @type {Client}
	* @readonly
	*/
	Object.defineProperty(this, 'client', { value: client });