feat(viewport-ruler): add common window resize handler

[crisbeto]

Adds the change method to the ViewportRuler, allowing for components to hook up to a common window resize handler.

BREAKING CHANGE: Previously the ScrollDispatcher.scrolled subscription would react both on scroll events and on window resize events. Now it only reacts to scroll events. To react to resize events, subscribe to the ViewportRuler.change() stream.

[mmalerba]

caretaker note: unexpected screenshot failures, verify global presubmit ok before merging

[googlebot]

CLAs look good, thanks!

[crisbeto]

Sorry for the email spam everyone, faulty rebase.

[angular-automatic-lock-bot]

This issue has been automatically locked due to inactivity.
Please file a new issue if you are encountering a similar or related problem.

Read more about our automatic conversation locking policy.

_{This action has been performed automatically by a bot.}