fix(TextArea): correct value type in onChange/onInput callback data

[Khushighosh]

Fixes #4464

The onChange/onInput callbacks for TextArea were typed with data: TextAreaProps, which allows value to be number | string | undefined — reflecting valid input values. But at runtime, the callback always returns the actual typed string, so this made consumers cast/narrow data.value unnecessarily.

This PR introduces a TextAreaOnChangeData type that narrows value to string specifically for the callback's returned data, without changing StrictTextAreaProps.value itself.

[vercel]

@Khushighosh is attempting to deploy a commit to the Semantic UI Team on Vercel.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.53%. Comparing base (e0a42b5) to head (027ccdd).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4542   +/-   ##
=======================================
  Coverage   99.53%   99.53%           
=======================================
  Files         186      186           
  Lines        3463     3463           
=======================================
  Hits         3447     3447           
  Misses         16       16           

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