Add CSS vars for breakpoints

[mcoker]

We removed the CSS vars for breakpoints since we can't use them in @media queries, and left only the scss vars. We need to add those back since the react repo uses the CSS vars as a means to get the breakpoint values to do fancy pants scripty things like resize observer, and I imagine products may, too.

https://github.com/patternfly/patternfly-react/blob/029351e0fa402c80a6199e2bd4b28e8c06f17562/packages/react-core/src/components/Page/Page.tsx#L4C8-L4C26

https://github.com/patternfly/patternfly-react/blob/029351e0fa402c80a6199e2bd4b28e8c06f17562/packages/react-core/src/components/Page/Page.tsx#L163-L197

[srambach]

Also - let's see if they can be added as a token coming from Figma so they span design-dev.

[patternfly-build]

🎉 This issue has been resolved in version 6.0.0-alpha.128 🎉

The release is available on:

• GitHub release
• npm package (@alpha dist-tag)

Your semantic-release bot 📦🚀

[mcoker]

closed via #6636