AppSideNav - Component branch (HDS-3800)

[KristinLBradley]

📌 Summary

If merged, this PR will add the AppSideNav component to HDS but will not publish it. It will also un-publish the related AppHeader component. (See related memo)

🛠️ Detailed description

The majority of code was duplicated from the SideNav and then modified to implement the new AppSideNav component.

Major differences of note:

• The AppSideNav has an updated visual design using lighter colors than the SideNav
  • Dark theme styles are no longer added to nested Button & Dropdown components
• The AppSideNav structure was simplified:
  • Structural named blocks were removed: :header, :footer, :body, :root
  • The :logo & :actions child named blocks were removed (used in old :header)
  • The Header and Header::HomeLink child components were removed.
• The Navigator Narrator (skip link) was removed as the AppSideNav is meant to always be paired with the AppHeader which already includes this
• Bug with overflow scrolling was fixed (caused by navigating from panel with long content to panel with short content)

(Spike of restructured List and ListTitle which may be explored in later iterations)

(Internal references: RFC, Meta CRD)

🔗 External links

• Jira ticket: HDS-3800
• Figma file

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👀 Component checklist

• Percy was checked for any visual regression
• [ ] A changelog entry was added via [Changesets] (Removed changelog as component will not be published) (https://github.com/changesets/changesets) if needed (see templates here)

💬 Please consider using conventional comments when reviewing this PR.

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[alex-ju]

left a few suggestions. considering the age of this branch, I suggest we rebase before we get this in. let me know if you'd like me to handle this on your behalf

KB: Thanks! I had already rebased previously and I don't see any new changes in main.