Snackbar: misc improvements

[ciampo]

Following up from #45472

• [ ] SnackbarList is not very well-documented (it doesn't even have a README) and prior to this PR, didn't have Storybook examples either. We should re-organize the folder structure, improve the docs and come up with a better Storybook strategy (e.g. use subcomponents and merge Snackbar and SnackbarList in the same file)
• [x] We should refactor the Notice component to TypeScript and re-use its types in Snackbar
• [ ] I came across a framer-motion bug when clicking rapidly on two Snackbars in a list — the second Snackbar goes transparent but doesn't get fully removed
• [ ] The timeout logic for Snackbar to be dismissed works in a bit of an unexpected way (snackbar items don't get dismissed in order
• [ ] The isDismissible prop from notice data is not taken into account by Snackbar (although this could be on purpose)
• [ ] The Snackbar icon (passed through its icon prop) is not vertically centered, doesn't seem to work well with WordPress icons

[github-actions[bot]]

Hi, This issue has gone 180 days without any activity. This means it is time for a check-in to make sure it is still relevant. If you are still experiencing this issue with the latest versions, you can help the project by responding to confirm the problem and by providing any updated reproduction steps. Thanks for helping out.

[ciampo]

Still relevant