Block library: Isolate order-sensitive test interactions

[ciampo]

What?

Follow up to #80855 by isolating Columns test fixtures and loading the popover styles required by the Cover Browser tests.

Why?

Columns tests replaced a shared array. Seed 80855 also exposed a Cover fixture defect: the Full height toolbar button intercepted the content-position grid click because the fixture did not load the popover stacking styles. The content-position case passed alone but failed in the shuffled file. Resetting the pointer did not fix it.

How?

Columns uses local inputs. Cover imports the existing Popover and block-popover styles that WordPress normally enqueues separately. Both original pointer clicks and all assertions remain intact. The previous keyboard workaround is removed.

Testing Instructions

npm run test:unit:vitest -- packages/block-library/src/columns/test/utils.js packages/block-library/src/cover/test/edit.browser.test.js
npm run test:unit:vitest -- --sequence.shuffle.files --sequence.shuffle.tests --sequence.seed=80855 packages/block-library/src/columns/test/utils.js packages/block-library/src/cover/test/edit.browser.test.js

Repeat the Cover run with seeds 80856 and 80857. The toolbar must not intercept the matrix click, and the existing content-position assertions must pass.

Testing Instructions for Keyboard

No production UI changes. Existing keyboard cases are unchanged; content-position selection retains pointer coverage.

24 September rebase verification

Rebased onto the updated #83099 without changing this PR's patch. All 47 affected tests passed file and test shuffling at seeds 80855, 80856, and 80857. Focused lint and diff checks passed. The stack's production build passed on trunk b40716dc70b3; this PR changes test fixtures only.

New-trunk refresh

Includes trunk's stricter console accounting (#83095). All 47 affected tests passed again with seeds 80855 and 80856. Both repair patches and assertions are unchanged.

Use of AI Tools

Codex reproduced the failures, performed an independent adversarial review, repaired the fixture setup, and ran verification.

[github-actions]

🤖 PR meta 🤖

📦 Bundle size

Size Change: 0 B

Total Size: 8.22 MB

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[github-actions]

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Co-authored-by: ciampo <mciampini@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>

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