feat: implement Markdown and HTML page imports (#85)

* page import feature
* make file interceptor common

* replace @tiptap/html
* update tiptap version

* reduce table margin

* update tiptap version

* switch to upstream drag handle lib (fixes table dragging)

* WIP

* Page import module and other fixes

* working page imports

* extract page title from h1 heading

* finalize page imports

* cleanup unused imports

* add menu arrow

apps/server/src/common/helpers/prosemirror/html/generateHTML.ts

@@ -0,0 +1,21 @@
+import { Extensions, getSchema, JSONContent } from '@tiptap/core';
+import { DOMSerializer, Node } from '@tiptap/pm/model';
+import { Window } from 'happy-dom';
+
+export function generateHTML(doc: JSONContent, extensions: Extensions): string {
+  const schema = getSchema(extensions);
+  const contentNode = Node.fromJSON(schema, doc);
+
+  const window = new Window();
+
+  const fragment = DOMSerializer.fromSchema(schema).serializeFragment(
+    contentNode.content,
+    {
+      document: window.document as unknown as Document,
+    },
+  );
+
+  const serializer = new window.XMLSerializer();
+  // @ts-ignore
+  return serializer.serializeToString(fragment as unknown as Node);
+}