[EuiContextMenu] Support new renderItem custom content in items arrays

[cee-chen]

Summary

closes #7507

Example usage:

const CustomComponent = () => (
  <div data-test-subj="custom">Hello world</div>
);

<EuiContextMenu
  initialPanelId={1}
  panels={[
    {
      id: 1,
      title: 'Testing renderItem',
      items: [
        // Default context menu item
        {
          name: 'Renders an EuiContextMenuItem',
          panel: 2,
        },
        // Custom items
        {
          renderItem: () => <h3>Subtitle</h3>,
        },
        {
          key: 'custom',
          renderItem: CustomComponent,
        },
      ],
    },
  ]}
/>

This API intentionally matches EuiCollapsibleNavBeta.Item's API (see #7228 and elastic/kibana#167326).

QA

• Go to https://eui.elastic.co/pr_7510/#/navigation/context-menu#using-panels-with-mixed-items-content
• Click either popover button and confirm the custom popover footer + button renders as expected

General checklist

• Browser QA
  • Checked in Chrome, Safari, Edge, and Firefox
• Docs site QA
  • Updated documentation
  • [ ] Props have proper autodocs (using @default if default values are missing) and playground toggles - the typescript inferred prop for this sucks because it uses ExclusiveUnion, not sure if there's anything we can do about that
• Code quality checklist
  • Added jest and cypress 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)
• Designer checklist - N/A

[tkajtoch]

[Not a change request] We should simplify the type here someday and find a way to render an understandable definition in the props table

[cee-chen]

To clarify, ExclusiveUnion<> is already pretty terrible in our current props table (https://eui.elastic.co/v93.0.0/#/navigation/context-menu) - but we should definitely make this a tech debt item for some day!

[tkajtoch]

The changes look great!

[kibanamachine]

Preview staging links for this PR:

• Docs site: https://eui.elastic.co/pr_7510/
• Storybook: https://eui.elastic.co/pr_7510/storybook

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 2d7192b

History

• 💚 Build #1363 succeeded 2ce3373
• 💔 Build #1361 failed 2c3c923