Notebook Tokenization Fixes (#7375)

* Fix don't like; unclear if grammar necessssary too

* Cleanup and sanity check

* Cleanup and sanity check

* Add test

* Call onBeforeAttached for 3 types of editor models

extensions/notebook/package.json

@@ -161,6 +161,13 @@
         "configuration": "./language-configuration.json"
       }
     ],
+    "grammars": [
+      {
+        "language": "notebook",
+        "scopeName": "source.notebook",
+        "path": "./syntaxes/notebook.tmLanguage.json"
+      }
+    ],
     "menus": {
       "commandPalette": [
         {