Summary

This PR:

• Deprecates hideTitle prop in EuiFlyoutMenuProps. The menu title is now hidden by default for all flyouts. EuiFlyoutHeader will be the recommended way for visible titles instead. Prop is still honored.
• Removes flyoutMenuHideTitle computation inside useFlyoutMenu hook since this logic is no longer needed. We hide by default and only show title is prop is set to false, we can rely on the raw prop now.
• Adds a dev only warning when the prop is used.

Why are we making this change?

To enforce consistency between all flyouts and between main and child flyouts (previously, main flyouts hid titles by default and child showed them by default).

Closes https://github.com/elastic/kibana-team/issues/3017

Screenshots #

No changes for rows 1, 2, 5 (only warning)

Before	After

Testing checklist:

Storybook EuiFlyout > EuiFlyoutMenu > Playground:

• Default story shows flyout without title on its menu (hideTitle true)
• Toggle hideTitle to false, menu now renders with a title and header title is not rendered

Storybook EuiFlyout > Flyout Manager > Playground:

• Default story shows both main and child flyouts with a menu containing actions but no title
• Toggling both main and child flyouts showCustomActions results in both flyouts showing no menu (no visible menu title nor actions, menu hides)

Kibana flyout examples:
If you want to test in kibana follow these instructions to test kibana against this branch. Run kibana with yarn start --no-cache --run-examples to be able to test Flyout System Examples (reachable via global search bar)

• Add sample data, go to Discover, open a document Flyout and validate the flyout menu renders a title (this is currently the only Kibana consumer using hideTitle false)
• Open browser console and check for the console warning
• Search for flyout system examples in global search bar. Open main and child flyout. Validate none of them carry a menu with a title.
• Open browser console and check there is no console warning

Impact to users

Users setting the prop will notice no behavior change. Users not using the prop will notice that child flyouts now never render a title inside the flyout menu.

QA

Remove or strikethrough items that do not apply to your PR.

General checklist

• Browser QA
  • Checked in both light and dark modes
  • Checked in both MacOS and Windows high contrast modes
    • (emulate forced colors if you do not have access to a Windows machine.)
  • Checked in mobile
  • Checked in Chrome, Safari, Edge, and Firefox
  • Checked for accessibility including keyboard-only and screenreader modes
• Docs site QA
  • [~] Added documentation
  • Props have proper autodocs (using @default if default values are missing) and playground toggles
  • Checked Code Sandbox works for any docs examples
• Code quality checklist
  • Added or updated jest and cypress tests
  • Updated visual regression tests
• Release checklist
  • A changelog entry exists and is marked appropriately
  • If applicable, added the breaking change issue label (and filled out the breaking change checklist)
  • If the changes unblock an issue in a different repo, smoke tested carefully (see Testing EUI features in Kibana ahead of time)
• Designer checklist
  • If applicable, file an issue to update EUI's Figma library with any corresponding UI changes. (This is an internal repo, if you are external to Elastic, ask a maintainer to submit this request)