(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/ui2018/IconList.ts

@@ -113,6 +113,7 @@ export type IconName = "ChartArea" |
   "ResizePanel" |
   "Revert" |
   "RightAlign" |
+  "Robot" |
   "Script" |
   "Search" |
   "Settings" |
@@ -254,6 +255,7 @@ export const IconList: IconName[] = ["ChartArea",
   "ResizePanel",
   "Revert",
   "RightAlign",
+  "Robot",
   "Script",
   "Search",
   "Settings",