Add layout fill mode

[hichemfantar]

Why:

Introduce a new layout option 'fill' to enhance improve layout flexibility. Update related components to accommodate this new layout mode.

fill mode basically makes the main content take up all available space without discarding everything else unlike full mode

Closes: #4036

What's being changed (if available, include any code snippets, screenshots, or gifs):

tested all kinds of combinations with different types and everything works as expected with no regressions from my testing

type page, layout fill, toc true

type doc, layout fill, sidebar true, toc false

Check off the following:

• I have reviewed my changes in staging, available via the View
  deployment link in this PR's timeline (this link will be available after
  opening the PR).

[changeset-bot]

⚠️ No Changeset found

Latest commit: f383763

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
nextra-v2	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jan 28, 2025 9:56pm

1 Skipped Deployment

Name	Status	Preview	Comments	Updated (UTC)
nextra	⬜️ Ignored (Inspect)	Visit Preview		Jan 28, 2025 9:56pm

[vercel]

@hichemfantar is attempting to deploy a commit to the Vercel Team on Vercel.

A member of the Team first needs to authorize it.

[dimaMachina]

thanks for initial attempt, superseded by #4105 to make theme.toc configurable with layout: 'full'

[hichemfantar]

thanks