refactor: improve TypeScript definitions

[tien]

This PR fixes the following TypeScript issues:

• LiveChatLoaderProvider not accepting multiple children, fixed by typing children as ReactNode instead of JSX.Element
• Messenger component required explicitly passing providerKey prop like so <Messenger providerKey={undefined} />
• missing optional locale prop on LiveChatLoaderProps used by Facebook Messenger

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Name	Status	Preview	Updated
react-live-chat-loader	✅ Ready (Inspect)	Visit Preview	Sep 21, 2022 at 4:34AM (UTC)

[benschwarz]

Hey @tien, thanks for this. We recently updated TS types (see release 2.8.0) so this PR is no longer applicable. All the same, thanks for your contribution here. 💫