Update 12 col breakpoint from medium to large

[sowasred2012]

Done

• Updated the default breakpoint setting at which the layout switches to 12 columns
• Updated the breakpoint at which the side nav is displayed to match the above

Fixes #3209

QA

• Open demo
• Resize the browser, see that the layout doesn't break
• Compare to live site, see that the demo layout changes to 12 column at a wider breakpoint

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-4078.demos.haus

[lyubomir-popov]

If anything breaks it is likely going to be on ubuntu.com or another site that relies on the currentbreakpoints. Nevertheless I think we should procede with this and include qa steps in the upgrade guide.

[bartaz]

Maybe it should use $threshold-6-12-col? This way it would be connected to grid rather than screen size. I guess it may be closer to what we want.

[bartaz]

@sowasred2012 @lyubomir-popov While working on grid-based show/hide utils I started some exploration about vanilla breakpoints and how they relate to grid and utils. I feel like we may need more discussion on what we want to achieve to avoid fixing the symptoms.

Let's have some catch up call tomorrow.

[bartaz]

LGTM.

We will follow up on this one in #4081.