IBX-6773: [Tests] Used bookmark gateway constants instead of hardcoded table and column names

[vidarl]

🎫 Issue	n/a

Description:

Three tests referred to database tables and columns by string literal. The bookmark table was renamed from ezcontentbrowsebookmark to ibexa_content_bookmark between 4.6 and 5.0, so those literals did not survive the last merge up.
The gateway already exposes the names as constants: DoctrineDatabase::TABLE_BOOKMARKS and COLUMN_*.
Using them in LocationServiceTest and IsBookmarkedQueryBuilderTest keeps both tests correct across a rename, and keeps the expected sub-query in IsBookmarkedQueryBuilderTest in step with what the query builder actually produces.

IdSortClauseQueryBuilderTest had the same problem with the content item table, renamed from ezcontentobject to ibexa_content; it now uses Content\Gateway::CONTENT_ITEM_TABLE alongside the two table constants it already used. That one stayed unnoticed because the test asserts on the generated SQL without ever executing it.

For QA:

Documentation:

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[vidarl]

Re-requesting approval as I added one more commit, ref discussion in #834 (comment)