(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/common/Prefs.ts

@@ -104,6 +104,8 @@ export const DismissedPopup = StringUnion(
   'deleteRecords', // confirmation for deleting records keyboard shortcut,
   'deleteFields',  // confirmation for deleting columns keyboard shortcut,
   'tutorialFirstCard', // first card of the tutorial,
+  'formulaHelpInfo', // formula help info shown in the popup editor,
+  'formulaAssistantInfo', // formula assistant info shown in the popup editor,
 );
 export type DismissedPopup = typeof DismissedPopup.type;