MultiGadgetRepo is a wrapper around two or more GadgetRepos so that
they can be used at the same, facilitating migration from one repo to
another.
If a gadget appears in both repos, the definition in the first repo
takes precedence, and a warning is shown on Special:Gadgets.
This can be enabled to wrap GadgetDefinitionNamespaceRepo and
MediaWikiGadgetsDefinitionRepo by setting $wgGadgetsRepo to
'json+definition'. In this configuration, once a new JSON definition
exists for the same name, it is used instead of the old one, and the
old one can then safely be removed at a later time in the safe
knowledge that it is no longer used.
Adapted from If3cc5e22e9812d0fd1a9e8e269ea74a7f667dadd
Bug: T140323
Co-authored-by: Kunal Mehta <legoktm@debian.org>
Change-Id: Ibad53629e63ec8713d7a3b84a19838b94600588e
