test: Add visual regression tests for app layout

[jperals]

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.
• 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 97.59%. Comparing base (c2472a9) to head (51e92db).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4714   +/-   ##
=======================================
  Coverage   97.59%   97.59%           
=======================================
  Files         950      950           
  Lines       30655    30655           
  Branches    11234    11235    +1     
=======================================
  Hits        29919    29919           
+ Misses        729      689   -40     
- Partials        7       47   +40     

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[jperals]

Note: this test description in the internal package is called "with tooltip on hover in visual refresh", but the test is run for all systems and themes without distinction, including Classic , so I am dropping the "in visual refresh" part (which is not the special case anymore anyway)