Bundled Themes: Twenty Nineteen editor style interferes with navigation menu block.

Update editor styles to prepare for changes coming to the editor in 5.5. Currently the issue is only present when using the latest version of the Gutenberg plugin.

Props kjellr, Joen.
Fixes #49613.
Built from https://develop.svn.wordpress.org/trunk@47587


git-svn-id: https://core.svn.wordpress.org/trunk@47362 1a063a9b-81f0-0310-95a4-ce76da25c4cd