fix: controlled combobox with downshiftProps

[Neues]

Closes #18212

ensure onChange is called when downshiftProps & onStateChange is provided

Changelog

Changed

• spread downshiftProps before defining onStateChange
• call downshiftProps in onStateChange if it exists
• unit test

testing

• remove the args in the _fullyControlled example in ComboBox.stories.js (you need to do this to see console.logs for some reason)
• add a console.log to the onChange here
• add downshiftProps with onStateChange to the props of the ComboBox
  ie.

        downshiftProps={{
          onStateChange: () => console.log('onstatechange downshiftprops')
        }}

• verify that both the function provided to onStateChange and the function provided to onChange are firing.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.16%. Comparing base (5a0348c) to head (1b95483).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #18441   +/-   ##
=======================================
  Coverage   84.16%   84.16%           
=======================================
  Files         408      408           
  Lines       14449    14450    +1     
  Branches     4696     4666   -30     
=======================================
+ Hits        12161    12162    +1     
+ Misses       2124     2123    -1     
- Partials      164      165    +1     

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