feat: implement style api for textarea component

[mxschll]

Description

Extends the textarea component with a style API for customization, allowing developers to override default component styles.

Related links, issue #, if available: n/a

How has this been tested?

• Added unit tests for style prop validation and CSS class application
• Screenshot tests passed without visual regressions
• Added screenshot test coverage for pseudo selector style combinations (e.g., focus + hover) (CR-232301442)

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 97.20%. Comparing base (a59c74f) to head (078fd30).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4001   +/-   ##
=======================================
  Coverage   97.20%   97.20%           
=======================================
  Files         858      859    +1     
  Lines       25359    25404   +45     
  Branches     9014     9052   +38     
=======================================
+ Hits        24650    24695   +45     
- Misses        660      703   +43     
+ Partials       49        6   -43     

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[georgylobko]

[non-blocking] You can use the toggle button component instead

[mxschll]

Good point!