* Add automatic splitting of large metadata on upload or refresh. If
the reserializeMetadata option is enabled, metadata stored with PHP
serialization will be automatically reserialized to JSON.
* Inject configuration variable $wgUpdateCompatibleMetadata via
LocalRepo instead of accessing it directly.
* In refreshImageMetadata.php and rebuildImages.php, construct a new
LocalRepo with config overrides, instead of overwriting config
globals. Add a helper to RepoGroup to help with this.
* In refreshImageMetadata.php, add new options --convert-to-json and
--split which reserialize metadata and optionally split out large
items to blob storage.
Also, refreshImageMetadata.php was totally broken in the non-force mode
since metadata refresh on page view was disabled in b814245d9f. The
maintenance script was relying on newFileFromRow() magically upgrading
the row, which doesn't happen anymore. So, call maybeUpgradeRow()
directly.
Bug: T275268
Change-Id: I7bf7d9cef71641e287ca4346b568b381f4ada50e
9251f3c9e3