Remove markdown-it from js bundles

Remove markdown-it library from JS bundle
by replacing a prosemirror-markdown import
statement with an import statement that
only references the Markdown serializer module
in this library.

This change allows us to reduce the amount
of JavaScript required to deliver the
copy to gfm feature

app/assets/javascripts/behaviors/markdown/marks/bold.js

 /* eslint-disable class-methods-use-this */
 
-import { defaultMarkdownSerializer } from 'prosemirror-markdown';
 import { Bold as BaseBold } from 'tiptap-extensions';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 
 // Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
 export default class Bold extends BaseBold {

app/assets/javascripts/behaviors/markdown/marks/code.js

 /* eslint-disable class-methods-use-this */
 
-import { defaultMarkdownSerializer } from 'prosemirror-markdown';
 import { Code as BaseCode } from 'tiptap-extensions';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 
 // Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
 export default class Code extends BaseCode {

app/assets/javascripts/behaviors/markdown/marks/italic.js

 /* eslint-disable class-methods-use-this */
 
-import { defaultMarkdownSerializer } from 'prosemirror-markdown';
 import { Italic as BaseItalic } from 'tiptap-extensions';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 
 // Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
 export default class Italic extends BaseItalic {

app/assets/javascripts/behaviors/markdown/marks/link.js

 /* eslint-disable class-methods-use-this */
 
-import { defaultMarkdownSerializer } from 'prosemirror-markdown';
 import { Link as BaseLink } from 'tiptap-extensions';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 
 // Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
 export default class Link extends BaseLink {

app/assets/javascripts/behaviors/markdown/marks/math.js

 /* eslint-disable class-methods-use-this */
 
-import { defaultMarkdownSerializer } from 'prosemirror-markdown';
 import { Mark } from 'tiptap';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 import { HIGHER_PARSE_RULE_PRIORITY } from '../constants';
 
 // Transforms generated HTML back to GFM for Banzai::Filter::MathFilter

app/assets/javascripts/behaviors/markdown/nodes/blockquote.js

 /* eslint-disable class-methods-use-this */
 
-import { defaultMarkdownSerializer } from 'prosemirror-markdown';
 import { Blockquote as BaseBlockquote } from 'tiptap-extensions';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 
 // Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
 export default class Blockquote extends BaseBlockquote {

app/assets/javascripts/behaviors/markdown/nodes/bullet_list.js

 /* eslint-disable class-methods-use-this */
 
-import { defaultMarkdownSerializer } from 'prosemirror-markdown';
 import { BulletList as BaseBulletList } from 'tiptap-extensions';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 
 // Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
 export default class BulletList extends BaseBulletList {

app/assets/javascripts/behaviors/markdown/nodes/heading.js

 /* eslint-disable class-methods-use-this */
 
-import { defaultMarkdownSerializer } from 'prosemirror-markdown';
 import { Heading as BaseHeading } from 'tiptap-extensions';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 
 // Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
 export default class Heading extends BaseHeading {

app/assets/javascripts/behaviors/markdown/nodes/horizontal_rule.js

 /* eslint-disable class-methods-use-this */
 
-import { defaultMarkdownSerializer } from 'prosemirror-markdown';
 import { HorizontalRule as BaseHorizontalRule } from 'tiptap-extensions';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 
 // Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
 export default class HorizontalRule extends BaseHorizontalRule {

app/assets/javascripts/behaviors/markdown/nodes/image.js

 /* eslint-disable class-methods-use-this */
 
-import { defaultMarkdownSerializer } from 'prosemirror-markdown';
 import { Image as BaseImage } from 'tiptap-extensions';
 import { placeholderImage } from '~/lazy_loader';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 import { HIGHER_PARSE_RULE_PRIORITY } from '../constants';
 
 export default class Image extends BaseImage {

app/assets/javascripts/behaviors/markdown/nodes/list_item.js

 /* eslint-disable class-methods-use-this */
 
-import { defaultMarkdownSerializer } from 'prosemirror-markdown';
 import { ListItem as BaseListItem } from 'tiptap-extensions';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 
 // Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
 export default class ListItem extends BaseListItem {

app/assets/javascripts/behaviors/markdown/nodes/paragraph.js

 /* eslint-disable class-methods-use-this */
 
-import { defaultMarkdownSerializer } from 'prosemirror-markdown';
 import { Node } from 'tiptap';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 
 // Transforms generated HTML back to GFM for Banzai::Filter::MarkdownFilter
 export default class Paragraph extends Node {

app/assets/javascripts/behaviors/markdown/nodes/playable.js

 /* eslint-disable class-methods-use-this */
 /* eslint-disable @gitlab/require-i18n-strings */
 
-import { defaultMarkdownSerializer } from 'prosemirror-markdown';
 import { Node } from 'tiptap';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 
 /**
  * Abstract base class for playable media, like video and audio.

app/assets/javascripts/behaviors/markdown/nodes/text.js

 /* eslint-disable class-methods-use-this */
 
-import { defaultMarkdownSerializer } from 'prosemirror-markdown';
 import { Node } from 'tiptap';
+import { defaultMarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 
 export default class Text extends Node {
   get name() {

app/assets/javascripts/behaviors/markdown/serializer.js

-import { MarkdownSerializer } from 'prosemirror-markdown';
+import { MarkdownSerializer } from '~/lib/prosemirror_markdown_serializer';
 import editorExtensions from './editor_extensions';
 
 const nodes = editorExtensions

app/assets/javascripts/content_editor/services/markdown_serializer.js

+import { DOMParser as ProseMirrorDOMParser } from 'prosemirror-model';
 import {
   MarkdownSerializer as ProseMirrorMarkdownSerializer,
   defaultMarkdownSerializer,
-} from 'prosemirror-markdown/src/to_markdown';
-import { DOMParser as ProseMirrorDOMParser } from 'prosemirror-model';
+} from '~/lib/prosemirror_markdown_serializer';
 import Audio from '../extensions/audio';
 import Blockquote from '../extensions/blockquote';
 import Bold from '../extensions/bold';

app/assets/javascripts/lib/prosemirror_markdown_serializer.js

+export * from 'prosemirror-markdown/src/to_markdown';