[Inline Markdown] Build off main component improvements

[rshen91]

Summary

Blocked by inflight hover actions work

Closes #188910

This PR builds off of @ThomThomson's branch with his inline markdown work. This PR will merge after PR #187181 is merged.

This PR adds the Editor and Preview tabs for the inline markdown component

TODO

• Preview and Edit tabs
• Styling of the tabs is off - blocked by [Dashboard] Hover actions for panels #182535
• Styling the cancel and save buttons
• Tests
• Confirm accessibility

Checklist

Delete any items that are not applicable to this PR.

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• Flaky Test Runner was used on any tests changed
• Any UI touched in this PR is usable by keyboard only (learn more about keyboard accessibility)
• Any UI touched in this PR does not create any new axe failures (run axe in browser: FF, Chrome)
• If a plugin configuration key changed, check if it needs to be allowlisted in the cloud and added to the docker list
• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser)
• This was checked for cross-browser compatibility