Adds support for `flex`, `grid` and `column` layout techniques to the list of CSS attributes considered safe for inline CSS. The `\` character and CSS functions, eg `minmax()` are not yet supported.
Extends support of `border` properties to include `border-radius` and individual `background` properties to include all those implicitly supported by the shorthand attribute.
Props mrahmadawais, marybaum, birgire, peterwilsoncc, azaozz.
Fixes#37248.
See #47367.
git-svn-id: https://develop.svn.wordpress.org/trunk@46235 602fd350-edb4-49c9-b593-d223f7449a82
123c17536f