chore: add portal context

[francinelucca]

This pull request introduces a new PortalContext to the @primer/react library, allowing more flexible and context-driven control over where portal content is rendered. The changes include updates to the core Portal component, its exports, new Storybook examples, and additional tests to ensure correct behavior when using PortalContext and container overrides.

Changelog

New

• Added PortalContext to Portal.tsx, allowing consumers to specify a portalContainerName via React context, which determines the portal root container for content rendering. The Portal component now prioritizes the context value unless overridden by its own containerName prop.
• Added new tests in Portal.test.tsx to verify correct portal rendering behavior when using PortalContext, including context-only, default fallback, undefined context, and prop override scenarios.
• Added a Storybook example (WithPortalContext) in Portal.features.stories.tsx to demonstrate how to use PortalContext for controlling portal rendering, including context and prop override cases.

Changed

• Updated exports in index.ts and the package entry point to include PortalContext, making it available for consumers.

Removed

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Testing & Reviewing

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: 1884fcc

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	Minor
@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!

[francinelucca]

@copilot add tests to ensure elements render correctly inside custom Portal when PortalContext is supplied and on the default otherwise

[Copilot]

@francinelucca I've opened a new pull request, #6816, to work on those changes. Once the pull request is ready, I'll request review from you.

[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	89.62 KB (+0.11% 🔺)
packages/react/dist/browser.umd.js	89.56 KB (-0.06% 🔽)

[francinelucca]

@copilot add a storybook story that demonstrates how to use PortalContext to render items within a different Portal than the default

[Copilot]

@francinelucca I've opened a new pull request, #6821, to work on those changes. Once the pull request is ready, I'll request review from you.

[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!

[francinelucca]

@copilot fix the accessibility issue with the dark theme by using token background colors from the theme

[Copilot]

@francinelucca I've opened a new pull request, #6847, to work on those changes. Once the pull request is ready, I'll request review from you.

[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!

[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!