Make MediaViewer's main object accessible via mw.mmv.viewer
completed by: ☃ unicodesnowman
mentors: Gergő Tisza
MediaViewer displays images with associated metadata on top of wiki pages. It loads a bootstrap object on the domready event; the main Javascript object is lazy-loaded when the user clicks on an image.
The bootstrap object is available in the global Javascript scope for convenient debugging as mw.mmv.bootstrap, but there is no similar shortcut for the main object. (Actually there is, mw.mmv.bootstrap.viewer, but that's unintuitive.) Make it available as mw.mmv.viewer.
This is T76923 in Wikimedia's issue tracker.
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