Twenty Nineteen: avoid columns set to full width to extend beyond editor bounds.

This changeset applies `max-width` and `margin` CSS rules when `block-editor-writing-flow` and `editor-styles-wrapper` classes are on the same element.

Props charleyparkerdesign, sabernhardt, smit08, sclayf1.
Fixes #54169.


git-svn-id: https://develop.svn.wordpress.org/trunk@52925 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-content/themes/twentynineteen/style-editor.css

@@ -605,6 +605,7 @@ body .wp-block.aligncenter {
 }
 
 @media only screen and (min-width: 768px) {
+  body.block-editor-writing-flow,
   body .block-editor-writing-flow {
     max-width: 80%;
     margin: 0 10%;

src/wp-content/themes/twentynineteen/style-editor.scss

@@ -36,6 +36,7 @@ body {
 
 	@include media(tablet) {
 
+		&.block-editor-writing-flow,
 		.block-editor-writing-flow {
 			max-width: 80%;
 			margin: 0 10%;