Support IPv6 dev server URLs in legacy standalone RDT connection

Summary:
Changelog: [Internal]

A minimal tweak to a legacy code path for React DevTools in React Native (**NOT** Fusebox!) that enables it to work / not crash when encountering an IPv6 dev server address. See doc comment for more.

Reviewed By: hoxyq

Differential Revision: D77150288

fbshipit-source-id: c11c742aad7b83861a1242dd13c5ed2753fbdf29