Restore context menus for collapsed breadcrumbs

[raunak-rpm]

Fixes #16764

When breadcrumbs overflow into the "..." menu due to narrow viewport width, the collapsed breadcrumb items lose their context menu (dropdown) functionality. This is a regression that affects navigation usability.

Root Cause

The breadcrumbs-overflow.js module was creating simple link items for the overflow menu without preserving the .dropdown-indicator element data that enables context menus on hover. The original breadcrumb items contain data-model, data-children, and data-href attributes that configure the dropdown behavior, but these were being discarded during the overflow menu generation.

Solution

This fix adds two helper functions following the same pattern used in jumplists.js:

1. mapContextMenuItems(items) - Transforms server response items to the dropdown item format expected by Utils.generateDropdownItems()

2. createContextMenuCallback(hasModel, hasChildren, href) - Creates a lazy-loading callback that fetches context menu data on hover, supporting both "Actions" (contextMenu) and "Navigation" (childrenContextMenu) sections

After generating the overflow menu items, the fix iterates through collapsed breadcrumb items, detects those with .dropdown-indicator elements, extracts the relevant data attributes, and attaches nested tippy dropdowns that fetch context menu data on mouseenter.

Testing done

• Built the WAR file successfully with mvn -am -pl war,bom -Pquick-build clean install
• Webpack build completed successfully with no errors
• ESLint passes with no violations
• Verified the development server starts correctly with mvn -pl war jetty:run
• Manual testing: Created nested folder structure, resized browser to trigger breadcrumb overflow, confirmed context menus appear on hover over collapsed items

Proposed changelog entries

• Restore context menu functionality for breadcrumbs collapsed into the overflow menu

Proposed changelog category

/label regression-fix, web-ui

Proposed upgrade guidelines

N/A

Submitter checklist

• The issue, if it exists, is well-described.
• The changelog entries and upgrade guidelines are appropriate for the audience affected by the change (users or developers, depending on the change) and are in the imperative mood (see examples). Fill in the Proposed upgrade guidelines section only if there are breaking changes or changes that may require extra steps from users during upgrade.
• There is automated testing or an explanation as to why this change has no tests.
• New public classes, fields, and methods are annotated with @Restricted or have @since TODO Javadocs, as appropriate.
• New deprecations are annotated with @Deprecated(since = "TODO") or @Deprecated(forRemoval = true, since = "TODO"), if applicable.
• UI changes do not introduce regressions when enforcing the current default rules of Content Security Policy Plugin. In particular, new or substantially changed JavaScript is not defined inline and does not call eval to ease future introduction of Content Security Policy (CSP) directives (see documentation).
• For dependency updates, there are links to external changelogs and, if possible, full differentials.
• For new APIs and extension points, there is a link to at least one consumer.

Desired reviewers

@timja @janfaracik

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Pull request overview

This PR restores context menu functionality for breadcrumb items that overflow into the "..." menu when the viewport is narrow. The fix implements lazy-loading dropdown menus that fetch context menu data on hover, following the same pattern used in jumplists.js.

Changes:

• Added two helper functions (mapContextMenuItems and createContextMenuCallback) that mirror the pattern in jumplists.js for transforming server response items and creating lazy-loading dropdown callbacks
• Enhanced the overflow menu generation to detect breadcrumb items with dropdown indicators and attach nested tippy dropdowns that preserve the original context menu functionality

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[janfaracik]

Happy to hear others thoughts, but I'm not sure if this is needed. I think the scenario where a desktop user has collapsed breadcrumbs and wants to access their submenu is slim - I also think that breadcrumbs having submenus in the first place is a poor UX, and wouldn't want to extend it for this.

[MarkEWaite]

I plan to close this pull request after a 24 hour waiting period because it is failing to compile on ci.jenkins.io and the pull request submitter has not taken action to correct the mistake. I agree with @janfaracik that I don't think this is needed. That offers yet another reason to close the pull request.

@raunak-rpm if you intend for this to be reviewed further, you need to fix the issue that is causing the build to fail on ci.jenkins.io.

[MarkEWaite]

Closing as abandoned by the submitter.