fix(textbox, select, textarea): ensure width is maintained when a flex item

[nuria1110]

fix #7718

Proposed behaviour

Add flex-grow: 1 to Select, FormField (Textbox) and Textarea outermost container to ensure they extend to maximum width available when rendered within a flexbox.

Current behaviour

Select, Textbox and Textarea components default to minimum content width when they are flex items.

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

See https://stackblitz.com/edit/parsium-carbon-starter-nglktc7h?file=src%2FApp.tsx for issue demo.
See new story InFlexContainer for fix in Textbox, Textarea and Select.