feat: Add useUnmount hook

[TomasEng]

Description

This pull request adds a new hook named useUnmount to the @studio/hooks library. It calls a given function when the component unmounts, like componentDidUnmount in class components. It will be used in the process editor to clean up the BPMN modeler instance when the editor unmounts.

I have added the skip-manual-testing label since the hook is not yet in use, so there is no way to test it manually. Anyways, the unit tests should be sufficient for verifying that this function works as expected.

Related Issue

• Adding and immediately removing tasks that have connected layoutSets will not delete layoutSet due to stale cache #13035

Verification

• Your code builds clean without any errors or warnings
• Relevant automated test added (if you find this hard, leave it and we'll help out)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.58%. Comparing base (ffec39a) to head (d9614ea).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14382   +/-   ##
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  Coverage   95.58%   95.58%           
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  Files        1869     1870    +1     
  Lines       24237    24244    +7     
  Branches     2786     2786           
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+ Hits        23167    23174    +7     
  Misses        814      814           
  Partials      256      256           

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