In preparation for 856718 where pinnableElement.js makes use of features.js,
move features.js and limitedWidthToggle.js out of the skins.vector.js module and
into the skins.vector.es6 module. This will make it easier to use by
pinnableElement.js without needing the es6 module to depend on the es5 module.
This does have the negative side-effect of causing the limited width feature to
not be supported by IE11 (and other non-ES6 browsers), however this tradeoff was
discussed with our product manager to be acceptable. Additionally, this
maintains the status quo as the toggle button does not currently show in IE11
(which may be a bug).
Bug: T322051
Change-Id: If0e8cb98deabe847c2cc71fddb90ca36d15e5f8f
