Rename "tab buttons" to "segmented control"

[andesol]

Done

• Rename scss files from "tab-buttons" to "segmented-control" (but keep the old classes for compatibility)
• Update documentation
• Add example for the "new" component

Fixes https://github.com/canonical-web-and-design/vanilla-squad/issues/1328

QA

• Open demo
• In the examples section, check that both "tab buttons" and "segmented control" work in its different variants.
• Review updated documentation:
  • Segmented control

Check if PR is ready for release

If this PR contains Vanilla SCSS code changes, it should contain the following changes to make sure it's ready for the release:

• PR should have one of the following labels to automatically categorise it in release notes:
  • Feature 🎁, Breaking Change 💣, Bug 🐛, Documentation 📝, Maintenance 🔨.
• Vanilla version in package.json should be updated relative to the most recent release, following semver convention:
  • if CSS class names are not changed it can be bugfix relesase (x.x.X)
  • if CSS class names are changed/added/removed it should be minor version (x.X.0)
  • see the wiki for more details
• Any changes to component class names (new patterns, variants, removed or added features) should be listed on the what's new page.
• Documentation side navigation should be updated with the relevant labels.

[webteam-app]

Demo starting at https://vanilla-framework-4410.demos.haus

[bartaz]

We probably mention vf-p-tab-buttons somewhere in the docs (at least in the import section) so we should update that.

[bartaz]

Added couple comments inline in the code.

[bartaz]

LGTM