feat(textarea): remove legacy FormField, Label and Input usage

[tamas-sage]

Proposed behaviour

Textarea should remove the remaining legacy wrapper dependency and keep the same layout and styling as before.

Current behaviour

Textarea no longer uses legacy FormField, Label, or Input, but it still relies on legacy InputPresentation and has some layout regressions.

Checklist

• Commits follow our style guide
• Related issues linked in commit messages if required
• Screenshots are included in the PR if useful
• All themes are supported if required
• Unit tests added or updated if required
• Playwright automation tests added or updated if required
• Storybook added or updated if required
• Translations added or updated (including creating or amending translation keys table in storybook) if required
• Typescript d.ts file added or updated if required
• Related docs have been updated if required

QA

• Tested in provided StackBlitz sandbox/Storybook
• Add new Playwright test coverage if required
• Carbon implementation matches Design System/designs
• UI Tests GitHub check reviewed if required

Additional context

Testing instructions