Flow needed bits of code in updateOneSearchIndexConfig.php, but can't extend from it because:
* maintenance scripts have `require_once RUN_MAINTENANCE_IF_MAIN;`
* private methods/properties that can't be extended
* statics, mostly referencing `Connection::*` data, which is specific to core MW data
* usage of `$wgCirrus*` globals
https://gerrit.wikimedia.org/r/#/c/164967/ (merged)
https://gerrit.wikimedia.org/r/#/c/164971/ (merged)
https://gerrit.wikimedia.org/r/#/c/164965/ (merged)
https://gerrit.wikimedia.org/r/#/c/164966/ (merged)
https://gerrit.wikimedia.org/r/#/c/164968/ (merged)
https://gerrit.wikimedia.org/r/#/c/164969/ (merged)
https://gerrit.wikimedia.org/r/#/c/175716/ (merged)
https://gerrit.wikimedia.org/r/#/c/175999/ (merged)
https://gerrit.wikimedia.org/r/#/c/176000/ (merged)
https://gerrit.wikimedia.org/r/#/c/176285/ (merged)
https://gerrit.wikimedia.org/r/#/c/176286/ (merged)
https://gerrit.wikimedia.org/r/#/c/176946/ (merged)
https://gerrit.wikimedia.org/r/#/c/177222/ (merged)
https://gerrit.wikimedia.org/r/#/c/177223/ (merged)
https://gerrit.wikimedia.org/r/#/c/177551/ (merged)
https://gerrit.wikimedia.org/r/#/c/179923/ (merged)
https://gerrit.wikimedia.org/r/#/c/179924/
https://gerrit.wikimedia.org/r/#/c/182824/
https://gerrit.wikimedia.org/r/#/c/182825/
https://gerrit.wikimedia.org/r/#/c/183040/
https://gerrit.wikimedia.org/r/#/c/183267/
https://gerrit.wikimedia.org/r/#/c/183268/
https://gerrit.wikimedia.org/r/#/c/183269/
https://gerrit.wikimedia.org/r/#/c/183313/
https://gerrit.wikimedia.org/r/#/c/183533/