Bring over the ES and Less implementation from ooui-js and rename to
fit it into the VE hierarchy, but don't make any other substantial
changes.
Inlines the wikimediaui-themed styles, ignoring apex styles, and
hardcodes the Less constants.
Bug: T310865
Change-Id: Id43dafdf11c5df0d7d78112e5f62a8599bdbc879
