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).

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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