chore: Tolerate matchMedia returning null

[jperals]

Description

Support for matchMedia should be more than good enough (MDN docs), but it is returning null sometimes for some team's canaries, causing operational pain.

See AWSUI-61447.

Aiming to refactor by moving useMobile into component-toolkit (cloudscape-design/component-toolkit#173, cloudscape-design/component-toolkit#174), but that is taking longer, so I will do that on the side and expedite this fix in this form first.

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.
• 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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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.99%. Comparing base (a79c3a7) to head (eeb4361).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #4028 +/- ##
=======================================
Coverage 96.99% 96.99% =======================================
Files 861 861 Lines 25214 25213 -1 Branches 9094 9094 =======================================
Hits 24456 24456 + Misses 711 710 -1 
Partials 47 47 

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