Added note describing expected behaviour

Use mobile collapsing behaviour at width 1200px

Adds the collapsed mixin to the styling for .nav-sidebar
ensuring the nav-sidebar is collapsed on load via media
queries. Removes the need for an intermediate class to
collapse the sidebar on mobile viewports

Updated toggleCollapsedSidebar to check for desktop breakpoint

Adds the sidebar-collapsed-mobile class to the haml layouts
and sets media queries to display the sidebar collapsed by
default for sreen sizes greater than `sm` and less than `lg`

This reverts merge request !19873

i18n

fixed pipeline request throwing an error

See https://gitlab.com/gitlab-org/gitlab-ce/issues/42908

Closes #37972