Accessibility: Login and Registration: Respect the `prefers-reduced-motion`...

Accessibility: Login and Registration: Respect the `prefers-reduced-motion` media query for "shake" CSS animation on login failure.

This shake should not occur when the user has opted to reduce motion, for example by selecting the "Reduce motion" option in macOS' preferences or unselecting "Show animations in Windows" in Windows' preferences.

Follow-up to [47226].

Props eddystile, johnbillion, sabernhardt, afercia, audrasjb.
Fixes #49723.
Built from https://develop.svn.wordpress.org/trunk@47813


git-svn-id: https://core.svn.wordpress.org/trunk@47589 1a063a9b-81f0-0310-95a4-ce76da25c4cd