[Dialog] Add optional Title and Description parts

[benoitgrelard]

Closes #729

This PR:

• brings Title and Description from AlertDialog into Dialog itself
• improves upon existing dev warnings with new requirements
  • description is optional for Dialog but required for AlertDialog so that's reflected in the warnings
  • "localizes" the messages based on which primitive it is
  • links to docs

[jjenzz]

Some initial feedback to discuss. I'll finish reviewing when we've decided the outcome of this in case things change.

[jjenzz]

👍 looking good. Just one little nit that I'll leave up to you 😛

[jjenzz]

nit: Can we expose just LabelWarningProvider instead please? It looks like we only need the provider externally and we could also simplify consumption then:

const LabelWarningProvider: React.FC<LabelWarningContextValue> = props => {
  return <LabelWarningContext.Provider value={props} />;
}

<Dialog.LabelWarningProvider contentName="" titleName="" docsSlug="">
</Dialog.LabelWarningProvider>

vs

<Dialog.LabelWarningContext.Provider value={React.useMemo(() => ({ contentName: '', titleName: '', docsSlug: '' ), [])}>
</Dialog.LabelWarningContext.Provider>

I'm not too bothered about doing the memoization internally though, it was more Dialog.LabelWarningProvider vs Dialog.LabelWarningContext.Provider that was bothering me so the following would suffice if you prefer 😅

const LabelWarningProvider = LabelWarningContext.Provider;
export { LabelWarningProvider };

[benoitgrelard]

I went with the latter, because the former was missing the fact it should render children which brings us back in the same situation as createContext.