e2e tests: fix tests compatibility for WP 6.2

[priethor]

What

Fixes the e2e suite so that it also works with WordPress 6.2

Why

SCF requires a minimum WordPress version of 6.2, but the wp test utils we are using don't support older versions

How

• Creating an extended editor object that provides compatible ways to get:
  • The preview page (the button text changed in WP 6.3)
  • The canvas (there was no iframe in 6.2)
• Switching term/user tests from ID selectors to text locators

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 10.98%. Comparing base (6d201a1) to head (a31f266).
⚠️ Report is 2 commits behind head on trunk.

Additional details and impacted files

@@             Coverage Diff             @@
##             trunk     #271      +/-   ##
===========================================
+ Coverage     9.37%   10.98%   +1.61%     
  Complexity    4288     4288              
===========================================
  Files          266      266              
  Lines        33159    33159              
===========================================
+ Hits          3108     3642     +534     
+ Misses       30051    29517     -534     

Flag	Coverage Δ
e2e	29.55% <ø> (+7.72%)	⬆️
phpunit	6.08% <ø> (ø)

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[priethor]

Confirming tests pass in CI against WP 6.2, reverting to use latest.

[github-actions]

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Props priethor.

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