Previously, every time the drawer re-rendered a new entry animation may
be triggered. This PR fixes this by setting the open state to
`modalState[slug]?.isOpen` instead of `false`.
Additionally, I was able to simplify this component while maintaining
functionality. Got rid of one `useEffect` and one `useState` call. The
remaining useEffect also runs less often (previously, it ran every time
`modalState` changed => it re-ran if _any_ modal opened or closed, not
just the current one)
cb3f9bb3e9