Instead now pointing to the most recent Wayback Machine archive copy.

* Bump supported browsers for v5

- Chrome history: https://en.wikipedia.org/wiki/Google_Chrome_version_history
- Firefox latest ESR (v60): https://www.mozilla.org/en-US/firefox/organizations/
- Edge history: https://en.wikipedia.org/wiki/Microsoft_Edge#Release_history
- Desktop Safari history: https://en.wikipedia.org/wiki/Safari_version_history
- Opera history: https://help.opera.com/en/opera-version-history/

* Update .browserslistrc

* Roll back Chrome several versions for now

Still WIP, but wanting to get this merged, so finding a slightly wider baseline

* Migration docs page for v5

* Add JS section, tweak some copy

* Update migration.md

- `background-position: 0 0;` is the default background position, so redundant
- The background position should only be animated in the x direction
- `0%` is a little shorter than `from`

- Line height & font family from html were directly overridden by body, so they were redundant thus removed
- The remaining properties are moved to body
- Shim for IE10 tags removed
- hr cleanup
  - Combined styles from reboot & type
  - Changed from borders to background
    - This allows us to keep the color inherited.
    - Opacity can be used to change the intensity
    - Size attribute will not change the height instead of making the hr look like an input field
  - Better variable names
- headings cleanup
  - Moved all element styling to reboot
  - Type will now extend the element styling. This way we will save some redundant code
- small & mark are also moved to reboot. type does not contain any element styling anymore
- font weight removed from small, this did not really made sense

Removed leftover from #27789

Extrapolates the previously used selector into a new mixin that only generates valid CSS by creating psuedo-classes for `valid` and `invalid`, and nothing else.

Fixes #28380.