Extract createCellEditor function

[seeM]

Another step to simplify #14264, and maybe also a generally useful step.

The diff looks huge but it is just a cut and paste into a new function. Diff might look better if you hide whitespace changes.

Release Notes

New Features

• N/A

Bug Fixes

• N/A

Validation Steps

@:positron-notebooks @:web.

[github-actions]

E2E Tests 🚀
This PR will run tests tagged with: @:critical @:positron-notebooks @:web

^{readme  valid tags}

[github-actions]

PETE's assessment 🧪

Verdict: 🟢 Adequate via existing coverage -- this is a pure cut-and-paste extraction of the editor-setup logic into createCellEditor, and the existing CellEditorMonacoWidget.vitest.tsx exercises every moved branch through the rendered widget.

What changed

• The entire editor-setup body inside useCellEditorWidget's useEffect was extracted verbatim into a new top-level createCellEditor(...) function in CellEditorMonacoWidget.tsx; the hook now just calls it and wires up disposal. No behavior change -- the early-bailout guard, option building, focus/blur edit-mode logic, multi-select, and resize handlers all moved intact.

Tests in this PR

• Unit (Vitest/Mocha) ✅ (existing coverage -- CellEditorMonacoWidget.vitest.tsx)
• Extension host ✅ (not applicable)
• E2E (Playwright) ✅ (not applicable -- refactor exercised by existing e2e under test/e2e/tests/notebooks-positron/)

Existing coverage

src/vs/workbench/contrib/positronNotebook/test/browser/notebookCells/CellEditorMonacoWidget.vitest.tsx renders CellEditorMonacoWidget (which calls useCellEditorWidget -> now createCellEditor) and asserts on the moved logic directly: editor attachment (attaches a code editor to the cell), contribution skip-list, Positron option overrides + live re-apply, dispose/detach on unmount, resize on layout and content-size change, edit-mode entry/exit on focus/blur including the overlay-guard and modifier-mousedown branches, and focus-restore paths. Because the function was moved without semantic changes, these tests fully pin the extracted code.

Suggested additions

None.

Suggested tags (optional)

None needed -- the PR body already carries @:positron-notebooks (a valid feature tag in test/e2e/infra/test-runner/test-tags.ts), so the notebook e2e suite under test/e2e/tests/notebooks-positron/ will run at PR time.

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[nstrayer]

Good stuff. Again with the CI failures being suspiciously located but almost assuredly flakes.

Definitely a good candidate for extraction/abstraction.