Updated strategy for empty newline sections

- For some reason, TinyMCE would handle empty paragraphs with a '&nbsp'
  by default but this would be removed when the paragraph had an
  attribute. This was fine in the old editor.
- This changes the approach to use '<br>' tags within elements
  for "spaced emptiness".
- For compatbility with any existing empty paragraphs, I updated the
  styles to show default height for empty paragraph sections.
- This also makes changes to help preserve encoded &nbsp; html tags
  since they were getting converted along the journey.

Related to #3302

resources/js/wysiwyg/config.js

@@ -243,6 +243,7 @@ export function build(options) {
         remove_script_host: false,
         document_base_url: window.baseUrl('/'),
         end_container_on_empty_block: true,
+        remove_trailing_brs: false,
         statusbar: false,
         menubar: false,
         paste_data_images: false,