(core) Implement AI Assistant UI V2

Summary:
Implements the latest design of the Formula AI Assistant.

Also switches out brace to the latest build of ace.

Test Plan: Browser tests.

Reviewers: jarek

Reviewed By: jarek

Subscribers: jarek

Differential Revision: https://phab.getgrist.com/D3949

package.json

@@ -116,13 +116,13 @@
     "@gristlabs/sqlite3": "5.1.4-grist.8",
     "@popperjs/core": "2.3.3",
     "accept-language-parser": "1.5.0",
+    "ace-builds": "1.23.3",
     "async-mutex": "0.2.4",
     "axios": "0.21.2",
     "backbone": "1.3.3",
     "bootstrap": "3.3.5",
     "bootstrap-datepicker": "1.9.0",
     "bowser": "2.7.0",
-    "brace": "0.11.1",
     "collect-js-deps": "^0.1.1",
     "color-convert": "2.0.1",
     "commander": "9.3.0",