Backport "Add size popover middleware to fix overflow issues in Popover.Dropdown" to v6

[ranquild]

Backports #5213

This PR backports the fix above to handle tall content in Popover.Dropdown. Reproduction https://codesandbox.io/s/amazing-nobel-s6zqy8

How to verify:

• yarn storybook
• Open http://localhost:7520/?path=/story/popover--size
• Click on the button and verify that it's possible to scroll the dropdown content properly

Issue (codesandbox):

Fix (storybook):

[rtivital]

Thanks!