chore: Move editor into codebase (#2930)

shared/editor/nodes/Doc.ts

@@ -0,0 +1,14 @@
+import { NodeSpec } from "prosemirror-model";
+import Node from "./Node";
+
+export default class Doc extends Node {
+  get name() {
+    return "doc";
+  }
+
+  get schema(): NodeSpec {
+    return {
+      content: "block+",
+    };
+  }
+}