(core) Floating formula editor

Summary:
Adding a way to detach an editor. Initially only implemented for the formula editor, includes redesign for the AI part.
- Initially, the detached editor is tight with the formula assistant and both are behind GRIST_FORMULA_ASSISTANT flag, but this can be relaxed
later on, as the detached editor can be used on its own.

- Detached editor is only supported in regular fields and on the creator panel. It is not supported yet for conditional styles, due to preview limitations.
- Old code for the assistant was removed completely, as it was only a temporary solution, but the AI conversation part was copied to the new one.
- Prompting was not modified in this diff, it will be included in the follow-up with more test cases.

Test Plan: Added only new tests; existing tests should pass.

Reviewers: JakubSerafin

Reviewed By: JakubSerafin

Differential Revision: https://phab.getgrist.com/D3863

app/client/models/DocPageModel.ts

@@ -375,7 +375,7 @@ export class DocPageModelImpl extends Disposable implements DocPageModel {
     const comparison = comparisonUrlId ?
       await this._api.getDocAPI(urlId).compareDoc(comparisonUrlId, { detail: true }) : undefined;
 
-    const gristDoc = gdModule.GristDoc.create(flow, this._appObj, docComm, this, openDocResponse,
+    const gristDoc = gdModule.GristDoc.create(flow, this._appObj, this.appModel, docComm, this, openDocResponse,
                                               this.appModel.topAppModel.plugins, {comparison});
 
     // Move ownership of docComm to GristDoc.