[html] fix convertLazyLoading: set img src to valid single url

[User123698745]

$img->src in convertLazyLoading is currently being set to an array of all srcset values. That is an invalid value. src must be a single url.
This PR splits the existing parseSrcset into parseSrcset without return_largest_url and parseSrcsetLargestImageUrl to make the intention more clear.
convertLazyLoading now uses parseSrcsetLargestImageUrl.
convertLazyLoading is mainly used by CssSelectorBridge and CssSelectorFeedExpanderBridge

[github-actions]

Pull request artifacts

Bridge	Context	Status
CssSelector	1 untitled (current)	❌ Bridge returned error 404! (20360) ❌ Type: HttpException ❌ Message: https://example.com/blog/ resulted in 404 Not Found
CssSelector	1 untitled (pr)	❌ Bridge returned error 404! (20360) ❌ Type: HttpException ❌ Message: https://example.com/blog/ resulted in 404 Not Found
CssSelectorFeedExpander	1 untitled (current)	❌ Bridge returned error 404! (20360) ❌ Type: HttpException ❌ Message: https://example.com/feed.xml resulted in 404 Not Found
CssSelectorFeedExpander	1 untitled (pr)	❌ Bridge returned error 404! (20360) ❌ Type: HttpException ❌ Message: https://example.com/feed.xml resulted in 404 Not Found

last change: Monday 2025-09-29 17:36:19