Fix animated multi-value select width bug

[lukebennett88]

Description

This PR fixes #5251 (where the width of selected item in a multi-value select could sometimes be far too wide if it was animated).

As an added bonus this refactors a class component into a function component.

Since useEffect fires after the first paint, the width that we get from getBoundingClientRect should always be correct.

Before:

React.Select.Animated.Width.Bug.Before.mp4

After:

React.Select.Animated.Width.Bug.After.mp4

In my testing I couldn't reliably reproduce the bug — before I made the changes, most of the time I could get bug to happen, but not always (you can see in the video about that it doesn't happen on my first attempt). After making the changes I haven't been able to reproduce it. I'm reasonably confident that this is fixed, but some extra eyes on this would be appreciated.

[changeset-bot]

🦋 Changeset detected

Latest commit: 436e250

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
react-select	Patch

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[Rall3n]

Easiest solution would have been to enforce flex layout if isMulti is set, as the problem probably stems from switching between grid and flex when the first option is being selected after typing at least one letter.

[lukebennett88]

Thanks @Rall3n, I've updated this PR to be much simpler now that I know what the root cause is 😅