Remove max layout width, update layout sidebar width, allow collapsible

[wibjorn]

Remove max layout width, update layout sidebar width, allow collapsible right container (aside) and update several components to fit this new approach. This entails changing the site header, heroes, a few more components to not apply the previous max width. Not that the mixins that apply media queries targeting widescreen are available for use elsewhere. See active changesets for more details.

Links:

• layouts
• site-header
• hero
• banner

Testing

1. Run locally.
2. Visit layout page. Toggle container labels on and/or open dev tools. Toggle containers while resizing to various screen sizes.
3. Visit other component documentation pages. Expand page content to be full width. Resize screen.

Contributor checklist

• Did you update the description of this pull request with a review link and test steps?
• Did you submit a changeset? Changesets are required for all code changes.
• Does your pull request implement complex UI logic (js/ts)? Consider adding an integration test to test your user flow.
• Does your pull request change any transforms? Did you test they work on right to left?

[changeset-bot]

🦋 Changeset detected

Latest commit: ddda5da

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
@microsoft/atlas-css	Major
@microsoft/atlas-site	Patch
atlas-design-system-tools	Patch

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