[regression] Restore IPE controls in Gin toolbar and Navigation top bar

Problem/Motivation

Layout Builder IPE previously displayed its editing controls in Gin’s toolbar at the top of the page. With recent versions of Drupal, Gin and Gin Layout Builder, the controls can instead appear only in the sidebar. This looks like a regression.

The sidebar is useful for revision information and other fields, but it takes up space and can be collapsed. Actions needed to save, preview or leave the editor should remain available at the top.

There are several cases to support. Gin can use the core Toolbar module, the core Navigation module or its own experimental Navigation mode. These use different code paths. Gin’s “Horizontal, Modern Toolbar” and “Legacy, Classic Drupal Toolbar” are also separate options.

Steps to reproduce

1. Install Drupal 11 with Layout Builder IPE, Gin, Gin Toolbar and Gin Layout Builder.
2. Use Gin as the administration theme.
3. Enable Layout Builder overrides and IPE for a content type.
4. Open a canonical entity page and click “Customize”.
5. Check where the Layout Builder and IPE controls are displayed.
6. Repeat with:
   • Core Navigation with Gin.
   • Gin’s “Horizontal, Modern Toolbar”.
   • Gin’s “Sidebar, Vertical Toolbar”.
   • Gin’s “Legacy, Classic Drupal Toolbar”.
   • Gin’s experimental “New Drupal Navigation” option without the core Navigation module enabled.

Proposed resolution

Restore the editing controls at the top of the page.

For the Toolbar variants, the IPE controls should be part of the toolbar as they were before. With Navigation, IPE should show the same Layout Builder controls as the normal Layout tab, with the additional IPE actions.

Revision information and other fields can remain in the collapsible sidebar. Closing the sidebar must not hide actions needed to work with or leave the editor.

The additional IPE buttons should have exactly the same style as the existing Gin Layout Builder buttons. Permissions and the existing button visibility settings must still be respected.

The implementation should share the handling of the actions between Toolbar and Navigation where that makes sense. It should not change the normal Layout tab or IPE without Gin Layout Builder.

Remaining tasks

• Create and review an MR.
• Test entering, closing, reopening and saving IPE.
• Test the preview, discard and revert controls.
• Test all Toolbar and Navigation configurations listed above.
• Test with the secondary toolbar enabled and disabled.
• Test desktop and mobile layouts with the sidebar open and closed.
• Test users without Toolbar or Navigation permission.
• Test the Gin Layout Builder button visibility settings.
• Test without Gin Layout Builder.
• Test the supported Drupal and Gin Layout Builder versions.
• Confirm that the normal Layout tab is unchanged.

User interface changes

Layout Builder and IPE actions are shown together at the top of the page. Revision information and other fields remain in the collapsible sidebar.

API changes

None intended.

Data model changes

None.