AnchoredOverlay: Add Popover API, modifications to CSS anchor positioning

[TylerJDev]

Prerequisite to https://github.com/github/primer/issues/6448, part of https://github.com/github/primer/issues/6431

Utilizes the Popover API to power our CSS anchor positioning in AnchoredOverlay. Both the popover support and CSS anchor positioning are behind the primer_react_css_anchor_positioning feature flag.

Changelog

New

• Adds popover support to AnchoredOverlay

Changed

• Small modifications, bug fixes towards CSS anchor positioning

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-ui (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: e2d5da9

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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[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.

[primer]

🤖 Lint issues have been automatically fixed and committed to this PR.

[primer-integration]

👋 Hi from github/github-ui! Your integration PR is ready: https://github.com/github/github-ui/pull/16560

[primer-integration]

⚠️ Integration PR Outdated

This integration PR does not have the latest commit from the primer/react PR.

Integration PR references: 5e39b869be8265f47ce2e8531eff8cc762a0f179
Latest commit on primer/react PR: 3686e5eaaeab8f9967e2fdab6bcac72e86835090

Please update the integration PR to reference the latest commit from the primer/react PR before reviewing workflow results.