Move over logic which isn't specific to the article
implementation of VE (e.g. nothing related to loading/saving).
Refactors setupSurface to use an abstract tracking method (which
does nothing by default), and moves surface CSS classes to #createSurface.
Breaking change:
* Rename onSurfaceReady to surfaceReady. We shouldn't need to listen
to our own events.
* Rename onReady to documentReady. onReady is not a listener.
Bug: T97166
Change-Id: I7242b1bb5501b7755a18a13d13e166c30cac9cdd
This makes way for a base mw.Target class which is
not specific to articles (e.g. Flow boards).
Bug: T97166
Change-Id: If72650bdf87aa9f195b004da0a4d815f1a8063a3