Editor: add support for style states on block instances.

Adds a "states" block support that allows styling pseudo states and viewport sizes.

Props isabel_brison, andrewserong, ramonopoly, audrasjb, desrosj.
Fixes #65239.


git-svn-id: https://develop.svn.wordpress.org/trunk@62453 602fd350-edb4-49c9-b593-d223f7449a82

Author: tellthemachines