Going into the new version of Vector, we'll want to rewrite the layout
rules entirely and decouple the sidebar from the logo.
To prepare for this we will move the layout file into a legacy folder.
We also separate Sidebar styles needed for the legacy mode from the old mode.
This will allow us to make changes to the header in new Vector without having to touch
or test the legacy codebase via a new file layout.less and using the existing sidebar
code.
Bug: T246170
Change-Id: Ieb4f8f2b2f0e4f48d76a210ab30acd08e3e83bcb
