[main] Add paginated vocabulary search with 'Show previous/next results' controls in hierarchical browse

[ZahraaChreim-Atmire]

References

• Fixes Hierarchical browse returns only first 20 results when searching/filtering #4500
• 7.x port is available at [dspace-7_x] Add paginated vocabulary search with 'Show previous/next results' controls in hierarchical browse #4504

Description

Added paging state management to the vocabulary treeview service, updating after each query based on whether previous or next pages exist; this state is exposed to the component to conditionally render navigation buttons in the hierarchical vocabulary browse.

Instructions for Reviewers

List of changes in this PR:

• First, added currentPage, totalPages, showNextPageSubject, and showPreviousPageSubject to the vocabulary-treeview.service to manage and expose pagination state.
• Second, created a new method searchByQueryAndPage(query, selectedItems, page) to support page-specific vocabulary search requests. The existing searchByQuery method was updated to call this with page 1 by default.
• Third, updated searchByQueryAndPage to extract pagination info from the search response and update the showNextPageSubject and showPreviousPageSubject based on whether more pages are available.
• Fourth, exposed showNextPage$ and showPreviousPage$ in the component, derived from showNextPageSubject, and showPreviousPageSubject, to reactively control the display of pagination buttons.
• Fifth, added conditional rendering of “Show next results” and “Show previous results” buttons in the template, along with loadNextPage and `loadPreviousPage to trigger paging behavior.

To test this PR:

1. Create a custom vocabulary XML file containing more than 20 nodes. Example: nodes with label="label1" through label="label100" and corresponding values like "value test 1" to "value test 100".
2. Deploy the vocabulary to your backend instance.
3. Navigate to the hierarchical browse interface in the UI (e.g., /browse/srsc).
4. Enter the query label.

Expected behavior after applying this PR:

• Only the first 20 matching entries are displayed initially.
• A “Show next results” button appears below the filtered tree.
• Clicking it displays the next 20 results and replaces the tree content.
• When on subsequent pages, a “Show previous results” button also appears to navigate back.
• On the final page, only the “Show previous results” button should be visible (no “Show next”).
• On the first page, only the “Show next results” button should be visible.

First page:

Intermediate page:

Last page:

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