Fix SRF "gallery format" overlay and redirect #977
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MediaWiki's evolution of its gallery HTML structure forces SRF to adapt.
MediaWiki has adopted a "mw-file-description" HTML class as more semantic and specific for file description links in gallery displays. It replaces the former, generic, "image" class applied to the same elements.
So, Semantic Result Formats - Gallery output needs to adapt specifically in its "overlay" and "redirect" options because they relied upon the old HTML output of MediaWiki.
If running this in a containerized / development environment, you can test only gallery-related functionality
"cd /var/www/html/extensions/SemanticResultFormats && composer phpunit -- --filter Gallery"
Fixes Issue #940 with explanation by @ADB-Linux