feat: Global theming APIs

[fralongo]

Description

Related links, issue #, if available: n/a

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates. N/A
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md. Yes
• Changes do not include unsupported browser features, see CONTRIBUTING.md. Yes
• Changes were manually tested for accessibility, see accessibility guidelines. N/A

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests? Yes
• Changes are covered with new/existing integration tests? Yes

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[codecov]

Codecov Report

❌ Patch coverage is 97.22222% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 97.42%. Comparing base (9c52a81) to head (5dd9821).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/theming/index.ts	97.22%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4559      +/-   ##
==========================================
- Coverage   97.42%   97.42%   -0.01%     
==========================================
  Files         938      938              
  Lines       29680    29716      +36     
  Branches    10788    10793       +5     
==========================================
+ Hits        28917    28952      +35     
- Misses        716      757      +41     
+ Partials       47        7      -40     

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[jkuelz]

Is there a reason we go straight to the top vs using the findUpAPI that already exists for plugins?

We also use getTopWIndow in our ErrorBoundary component.

There is also a key piece missing here that both of those have: the cross-origin SecurityError check -- which is only thrown when accessing writable properties on the window directly. We need to add that to the first statement to make the catch have any effect.

function getTopWindow(): WindowWithTheme {
    try {
      if (window.top && window.top.document) { // <-- this forces cross-orign to return the security error here
        return window.top as WindowWithTheme;
      }
    } catch {
      // Cross-origin top — fall back to current window.
    }
    return window as WindowWithTheme;

Should we use a shared utility here? We could've prevented this bug (and any future fixes that we may need to make).

[jkuelz]

Looks good, just one comment on the getTopWindow fn.