Try: zero width space in empty paragraph. (#28268)

This is a followup to https://github.com/WordPress/gutenberg/pull/27995/files#r557493964. It replaces the nonbreaking space character output in empty paragraphs, with a zero width space.

packages/block-library/src/paragraph/style.scss

@@ -38,5 +38,5 @@ p.has-text-color a {
 
 // Prevent an empty P tag from collapsing, so it matches the backend.
 p:empty::before {
-	content: "\a0";
+	content: "\200B";
 }