LiquidThreads extension

Analise where Article (not WikiPage) is really needed.

Expected result

• use WikiPage instead of multiple types of argument Page|WikiPage|Article
• use WikiPage instead of Article where is enough (after research and confirmation)

Examples:
\Threads::synchroniseArticleData()

WikipPage is enough:
\Threads::withSummary
\Threads::articleClause
\Threads::newThreadTitle

Done:
\Threads::withRoot() https://phabricator.wikimedia.org/T251360