dillon1000/react

[react-devtools-facade] 5/ support an already-installed DevTools hook (#36682)

Makes `installFacade` usable on pages that already have a DevTools
backend — most importantly the **React DevTools browser extension** — by
attaching to the existing `__REACT_DEVTOOLS_GLOBAL_HOOK__` instead of
refusing to install.

This is important, because otherwise if the page had Facade installed,
the user won't be able to use React DevTools browser extension.