Implementing field sizing option in TextArea component

[Copilot]

New field-sizing prop is now baseline: https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Properties/field-sizing. It allows for input controls to grow as needed. This would be a great opt-in for textarea.

https://www.youtube.com/watch?v=s48ueIHpG7A

[changeset-bot]

🦋 Changeset detected

Latest commit: d415af7

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/react	Minor

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[HiroAgustin]

@copilot rename prop fieldSizing to autoSize or something that makes more sense. Also update PR description.

[github-actions]

⚠️ Action required

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. Check the integration testing docs for step-by-step instructions. Or, apply the integration-tests: skipped manually label to skip these checks.

[Copilot]

@copilot rename prop fieldSizing to autoSize or something that makes more sense. Also update PR description.

Renamed the prop to autoSize across the API, docs, stories, tests, styles, and changeset. I also updated the PR description. Addressed in b92b3ef.

[Copilot]

Pull request overview

Adds an opt-in autoSize prop to Textarea that enables CSS field-sizing: content so the control can grow with its content, along with supporting docs/stories/tests and a changeset.

Changes:

• Added autoSize?: boolean to Textarea and exposed it via data-auto-size for styling hooks.
• Introduced a CSS Module rule applying min-height: 1lh and field-sizing: content when autosizing is enabled.
• Added Storybook controls/examples and docs metadata, plus a changeset entry.

Show a summary per file

File	Description
packages/react/src/Textarea/Textarea.tsx	Adds the autoSize prop and renders a data-auto-size attribute to toggle styling.
packages/react/src/Textarea/Textarea.test.tsx	Adds a test verifying autosize styling and that resize behavior remains unchanged.
packages/react/src/Textarea/Textarea.stories.tsx	Adds autoSize to Playground args and controls.
packages/react/src/Textarea/TextArea.module.css	Adds the [data-auto-size='true'] rule to enable field-sizing: content.
packages/react/src/Textarea/Textarea.features.stories.tsx	Adds an AutoSize feature story example.
packages/react/src/Textarea/Textarea.docs.json	Documents the new autoSize prop.
.changeset/textarea-auto-size.md	Adds a changeset for the new autoSize option.

Review details

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• Files reviewed: 7/7 changed files
• Comments generated: 1
• Review effort level: Lite

[Copilot]

Review details

• Files reviewed: 7/7 changed files
• Comments generated: 0 new
• Review effort level: Lite

[primer-integration]

Integration test results from github/github-ui PR:

  CI Passed
  VRT Passed
  Projects Passed

All checks passed!

[jonrohan]

❤️