[EuiFlyout] Introduce EuiFlyoutPluginContext for enhanced integration and deprecate legacy props

[paulinashakirova]

• Added EuiFlyoutPluginContext to facilitate external package integration with the flyout manager.
• Introduced menuBarSlot prop to replace the built-in Back button and history popover.
• Deprecated showBackButton, backButtonProps, and historyItems in favor of the new context.
• Updated EuiFlyoutMenu and related components to utilize the new context and props.
• Enhanced tooltip usage in the flyout menu for better accessibility and user experience.

Summary

API Changes

component / parent	prop / child	change	description

Screenshots

Before	After
{Before image}	{After image}

Impact Assessment

Note: Most PRs should be tested in Kibana to help gauge their Impact before merging.

• 🔴 Breaking changes — What will break? How many usages in Kibana/Cloud UI are impacted?
• 💅 Visual changes — May impact style overrides; could require visual testing. Explain and estimate impact.
• 🧪 Test impact — May break functional or snapshot tests (e.g., HTML structure, class names, default values).
• 🔧 Hard to integrate — If changes require substantial updates to Kibana, please stage the changes and link them here.

Impact level: 🟢 None / 🟢 Low / 🟡 Moderate / 🔴 High

Release Readiness

• Documentation: {link to docs page(s)}
• Figma: {link to Figma or issue}
• Migration guide: {steps or link, for breaking/visual changes or deprecations}
• Adoption plan (new features): {link to issue/doc or outline who will integrate this and where}

QA instructions for reviewer

Checklist before marking Ready for Review

• Filled out all sections above
• QA: Tested light/dark modes, high contrast, mobile, Chrome/Safari/Edge/Firefox, keyboard-only, screen reader
• QA: Tested in CodeSandbox and Kibana
• QA: Tested docs changes
• Tests: Added/updated Jest, Cypress, and VRT
• Changelog: Added changelog entry
• Breaking changes: Added breaking change label (if applicable)

Reviewer checklist

• Approved Impact Assessment — Acceptable to merge given the consumer impact.
• Approved Release Readiness — Docs, Figma, and migration info are sufficient to ship.

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: f049de7

cc @paulinashakirova

[elastic-vault-github-plugin-prod]

6 visual difference(s) found - expand to review, then click Approve visual changes to update baselines

euiflyout (4 differences)

Story	Before	After	Diff
manual return focus desktop
playground desktop
push flyouts desktop
menu bar example desktop

euipopover (1 difference)

Story	Before	After	Diff
playground desktop

euidatagrid (1 difference)

Story	Before	After	Diff
additional controls options desktop

[elasticmachine]

💔 Build Failed

• Buildkite Build
• Commit: f049de7
• Documentation website
• Storybook
• ❌ Visual regression tests failed (view diff table)

Failed CI Steps

• 📷 Test visual regression

History

cc @paulinashakirova