add basic yjs extension with baked in web rtc support (wip)

packages/extension-yjs/index.ts

@@ -0,0 +1,27 @@
+import { Extension } from '@tiptap/core'
+import { keymap } from 'prosemirror-keymap'
+import {
+  redo, undo, yCursorPlugin, ySyncPlugin, yUndoPlugin,
+} from 'y-prosemirror'
+import { WebrtcProvider } from 'y-webrtc'
+import * as Y from 'yjs'
+
+const ydoc = new Y.Doc()
+const provider = new WebrtcProvider('tiptap', ydoc)
+const type = ydoc.getXmlFragment('prosemirror')
+
+export default new Extension()
+  .name('yjs')
+  .plugins(() => {
+    return [
+      ySyncPlugin(type),
+      yCursorPlugin(provider.awareness),
+      yUndoPlugin(),
+      keymap({
+        'Mod-z': undo,
+        'Mod-y': redo,
+        'Mod-Shift-z': redo,
+      }),
+    ]
+  })
+  .create()