Improve Playwright test patterns in VariablePage (#63965) (#63979)

* Improve Playwright test patterns in VariablePage (#63965)

- Replace CSS :has-text() with locator.filter({ hasText }) in rowByKey
- Replace CSS attribute selector with getByRole('checkbox') in selectRow
- Replace page.waitForFunction() DOM queries with locator-based
  waiting (Promise.race of noData text vs first table row)
- Replace CSS input[type='checkbox'] with getByRole('checkbox')
  in selectAllCheckbox

Aligns with Playwright best practices per #63036.

* Revert checkbox selectors — Chakra hidden input incompatible with getByRole

getByRole('checkbox') resolves to Chakra UI's hidden <input> which
is not visible/stable, causing TimeoutError. Keep original CSS
selectors for checkbox interactions until Chakra components expose
proper accessible roles.

* Use expect().toBeVisible() with .or() combinator

Replace Promise.race + waitFor() with Playwright's built-in
.or() combinator for assertion-based waiting. Verified locally
with 5/5 pass.

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Co-authored-by: Jarek Potiuk <jarek@potiuk.com>