[Popover] Reverting exit timer to base duration

[dfmcphee]

WHY are these changes introduced?

In #4580 we changed the timeout on the unmounting of popovers to match the new instant transition. This created issues for some implementations and introduced race conditions.

WHAT is this pull request doing?

This reverts the exit timeout to the default duration base like it had before.

How to 🎩

🖥 Local development instructions
🗒 General tophatting guidelines
📄 Changelog guidelines

Copy-paste this code in playground/Playground.tsx:

import React from 'react';
import {Page} from '../src';

export function Playground() {
  return (
    <Page title="Playground">
      {/* Add the code you want to test in here */}
    </Page>
  );
}

🎩 checklist

• Tested on mobile
• Tested on multiple browsers
• Tested for accessibility
• Updated the component's README.md with documentation changes
• Tophatted documentation changes in the style guide
• For visual design changes, ping @ sarahill to update the Polaris UI kit

[github-actions]

size-limit report

Path	Size
cjs	166.08 KB (+0.01% 🔺)
esm	96.63 KB (+0.01% 🔺)
esnext	143.5 KB (+0.01% 🔺)
css	34.53 KB (0%)