Add automated test for "Filter Nested Document"

The manual test is here: Filter Nested Document

Existing automated coverage

• AllDocsIT#verifyAllDocs: Page Index 'Index' tab: filtering the Location column by a single-level page name returns exactly that page (validateFilterDoc), plus Last Author filter
• LiveDataIT#enforceRequiredRights: Filtering a livetable-source Live Data by the doc.title column (not the Page Index)
• LiveDataIT#livedataLivetableTableLayout: The computed-title footnote is displayed when such pages are listed and disappears when they are filtered out (generic Live Data, not the Page Index)
• LiveTableResultsTest#restrictLocationAndFilterByDocLocation: Unit level: HQL generated for a doc.location filter (WebHome vs terminal handling)

Missing automated coverage

• Create nested pages 1, 1/2 and 1/2/3 (WebHome pages)
• Open Page Index (AllDocsPage index tab) and filter the Location column by '1/2/'; assert only pages 2 and 3 are listed
• Filter the Title column by '1', '2' and '3' and assert the matching rows each time
• Create a page whose displayed title is computed (differs from the stored title) and assert, when it is in the results, the '1' marker and the computed-title footnote are shown in the Page Index

Suggested location: xwiki-platform-core/xwiki-platform-index/xwiki-platform-index-test/xwiki-platform-index-test-docker/src/test/it/org/xwiki/index/test/ui/docker/AllDocsIT.java

Found by comparing the XWiki 18.4.4 manual test runs against the automated tests on master (a0055f10a1a).