Remove sx and BoxWithFallback from the Spinner component

[liuliu-dev]

Remove sx and BoxWithFallback from the Spinner component
Closes #5819

sx usage, tracking here: https://github.com/github/primer/issues/5827

Rollout strategy

• Major release; if selected, include a written rollout or migration plan

[changeset-bot]

🦋 Changeset detected

Latest commit: 1cc55d6

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

This PR includes changesets to release 2 packages

Name	Type
@primer/react	Major
@primer/styled-react	Major

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[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github depends on. If you are GitHub staff, we recommend testing these changes with github/github using the integration workflow. Thanks!

[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	89.76 KB (+0.02% 🔺)
packages/react/dist/browser.umd.js	89.9 KB (+0.02% 🔺)

[Copilot]

Pull Request Overview

This PR removes the deprecated sx prop and BoxWithFallback wrapper from the Spinner component as part of ongoing efforts to simplify the component API and reduce dependencies on the styled-system approach.

• Removes sx prop and SxProp type from the main Spinner component
• Eliminates BoxWithFallback wrapper and StyledSpinner function in favor of direct component usage
• Maintains backward compatibility by adding a styled wrapper in the legacy styled-react package

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/react/src/Spinner/Spinner.tsx	Removes sx prop support and BoxWithFallback wrapper, simplifies component implementation
packages/styled-react/src/index.tsx	Adds backward-compatible Spinner wrapper with sx prop support for legacy usage
packages/react/src/Spinner/Spinner.docs.json	Updates component documentation to remove sx prop reference
packages/react/src/Spinner/Spinner.dev.stories.tsx	Updates dev story to use CSS class instead of sx prop
packages/react/src/Spinner/Spinner.dev.stories.module.css	Adds CSS module for dev story styling
.changeset/beige-shrimps-sleep.md	Documents breaking change for major version release

[github-actions]

👋 Hi, there are new commits since the last successful integration test. We recommend running the integration workflow once more, unless you are sure the new changes do not affect github/github. Thanks!

[primer-integration]

👋 Hi from github/github-ui! Your integration PR is ready: https://github.com/github/github-ui/pull/3048

[primer-integration]

🟢 ci completed with status success.