Improve accessibility in the pagination component

[bethcollins92]

Done

Improvements to the accessibility of our pagination component:

• Added &[aria-current='page'] to the is-active styles
• Wrapped all pagination examples in a <nav> with an aria-label so users know it's the pagination navigation
• Added aria-label="page x" to each of the pages, to be more descriptive about what the number means
• Added aria-current="page" to the active pages

Fixes #4256

QA

• Open demo
• Check nothing has broken on the pagination examples/docs
• Check with voiceover the pagination examples
• Accessibility documentation is currently being written so will be in a separate PR
• The p-navigation class should be on the <nav> element, but this will be addressed in this issue

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-4258.demos.haus

[bartaz]

LGTM, thanks!