The commit syncs the following changes from Gutenberg:
- Background images: add support for theme.json ref value resolution gutenberg#64128
- Background images: ensure appropriate default values gutenberg#64192
- Background image: ensure consistency with defaults and fix reset/remove functionality gutenberg#64328
These changes brings consistency to the default background image styles WordPress applies to user uploaded images, and adds support for ref resolution to "background" style properties.
Props andrewserong, aaronrobertshaw.
Fixes #61858
Built from https://develop.svn.wordpress.org/trunk@58936
git-svn-id: http://core.svn.wordpress.org/trunk@58332 1a063a9b-81f0-0310-95a4-ce76da25c4cd