Align dropdowns within the super sidebar

What does this MR do and why?

This applies the necessary left offset to the "Create" and user menus in the super sidebar for the dropdowns to be aligned with the sidebar instead of floating to the right.

Additionally, this hides the "Create" menu's tooltip when it is opened. Until now, the tooltip would stay visible as long as the menu is open.

Known caveat

It's possible for the user menu to overflow the super sidebar when it contains a long status. This could also happen when using GitLab in non-English languages. We'll be providing an option to limit the width in gitlab-ui#2209 (closed).

Screenshots or screen recordings

Menu	Before	After
"Create"
User

How to set up and validate locally

1. Enable the new nav:

   1. Enable the feature flag:

      echo "Feature.enable(:super_sidebar_nav)" | rails c

   2. Enable the user setting from the user dropdown:

      

2. Open the "Create" or user menu.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #390930 (closed)