chore: Generate test definitions

[jperals]

Description

Adds test definitions and builds them into the lib directory as part of the build process.

Doc: J5RmAnz6YwPa

Test definitions for two components (action card and alert) are added, but they are not run yet (for an example of that, see #4509). Once I can consume them internally I will add the rest.

How has this been tested?

Ran npm run build and inspected the test-definitions directory generated inside lib.

Review checklist

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

Correctness

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

Security

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

Testing

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

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[jperals]

These two files are inside test/definitions/visual because they are definitions of visual regression tests, but I intentionally named the build files and process after just "test definitions" and not specifically "visual test definitions" because this approach can be used for other tests, such as integration tests, if we later want to.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.42%. Comparing base (7c2631d) to head (168756d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4544   +/-   ##
=======================================
  Coverage   97.42%   97.42%           
=======================================
  Files         939      939           
  Lines       29645    29645           
  Branches    10772    10771    -1     
=======================================
  Hits        28883    28883           
- Misses        715      755   +40     
+ Partials       47        7   -40     

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