Fix sticky issue header position for super sidebar

What does this MR do and why?

• Add .page-with-contextual-sidebar selector for default --width calculations
• Add .page-width-super-sidebar specific --width calculations and left position
• Update nav_helper class applications to exclude contextual sidebar classes being added for show_super_sidebar?
• Update merge request sticky header width calculations

Screenshots or screen recordings

Before	After
CleanShot_2023-02-22_at_16.29.12	CleanShot_2023-02-22_at_17.00.28

MD up

Contextual sidebar

collapsed left sidebar + collapsed right sidebar

collapsed left sidebar + expanded right sidebar

Super sidebar

collapsed super sidebar + collapsed right sidebar

collapsed super sidebar + expanded right sidebar

XL up

Contextual sidebar

expanded left sidebar + collapsed right sidebar

collapsed left sidebar + collapsed right sidebar

expanded left sidebar + expanded right sidebar

collapsed left sidebar + expanded right sidebar

Super sidebar

expanded super sidebar + collapsed right sidebar

collapsed super sidebar + collapsed right sidebar

expanded super sidebar + expanded right sidebar

collapsed super sidebar + expanded right sidebar

How to set up and validate locally

• Enable the feature flag

Feature.enable(:super_sidebar_nav)

• Enable the "New navigation" setting toggle from the user dropdown

• View and Issue or MR and scroll down until sticky header displays
• Toggle sidebars and viewport sizes

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 #392824 (closed)