fix(workflow-form): the code editor button opens nothing in the Form View, which has no editor host #8760

What happened?

Two paths reach the canvas's code editor from the Form View, and neither can show it.

• The step panel renders the operator's real property frame, and in edit mode (panelLive) that frame is interactive, so a Python UDF step shows the ordinary code-editor button. Pressing it calls codeEditorService.vc.createComponent(...) (codearea-custom-template.component.ts:87), and the only thing that ever sets vc is the canvas (workspace.component.ts:188, its <ng-template #codeEditor>). Before perf(workflow): switch between a workflow's two views without reloading the page #8581 the Form View was a fresh page load, so vc was undefined and the click threw; since perf(workflow): switch between a workflow's two views without reloading the page #8581 the canvas-to-form switch routes, so vc is the destroyed canvas's ViewContainerRef (its ngOnDestroy clears the container but keeps the reference) and Monaco is created into a detached view -- nothing visible.
• An exposed code-editor property is not offered for exposure at all (NON_FORM_FIELD_TYPES, custom-formly-type.ts:26), and a workflow that carries one from before falls back to a plain editable control (CANVAS_ONLY_FORMLY_TYPES, custom-formly-type.ts:35).

Expected, in two steps. Interim: the button is not shown, or is disabled with a reason, in the Form View until the form has an editor host, so a click neither throws nor does nothing silently. Proper: the form gets its own editor host -- owned above both views, or handed over with the session the way #8581 hands the rest over, rather than by the canvas alone -- and supplies the operator id from the binding; the shared codearea component changes accordingly. Then the code editor can be offered for exposure and rendered in the form instead of a fallback.

Part of #8439 (item 1) and the Form View feature #8011. Raised by @mengw15 on #8436; the step-panel path was found while auditing #8581.

How to reproduce?

1. Open a workflow with a Python UDF operator on the canvas, then switch to the Form View with the Form View button (perf(workflow): switch between a workflow's two views without reloading the page #8581 routes).
2. Enter edit mode and open the UDF step's panel.
3. Click the code editor button: nothing appears. (Opening the Form View from a direct URL instead: an exception in the console on the click.)

Version/Branch

1.4.0-incubating-SNAPSHOT (main)

Commit Hash (Optional)

506397a

What browsers are you seeing the problem on?

Chrome

Relevant log output

No response