feat: add useTagGroup and other fixes

[silviuaavram]

Adds useTagGroup.
Mentions useMultipleSelection deprecation.
Other improvements suggested by copilot.

[Copilot]

Pull request overview

This PR introduces the new useTagGroup hook to Downshift, providing an accessible solution for building tag group components. The PR updates the downshift package to version 9.1.0-alpha.7, adds comprehensive documentation for the new hook, and updates existing hook documentation to reference the new tag group functionality.

Changes:

• Added useTagGroup hook import and export in ReactLiveScope for live code examples
• Updated downshift package to version 9.1.0-alpha.7 to support the new hook
• Created comprehensive documentation for useTagGroup with usage examples
• Updated useSelect, useCombobox, and useMultipleSelection documentation to include tag group integration examples and deprecation notices
• Restructured migration guide references across documentation files to include v9

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 12 comments.

Show a summary per file

File	Description
src/theme/ReactLiveScope/index.js	Added useTagGroup hook import and export for live code examples
package.json	Updated downshift version from ^8.3.2 to 9.1.0-alpha.7
docs/hooks/useTagGroup.mdx	New documentation file for useTagGroup hook with basic usage example
docs/hooks/useSelect.mdx	Added tag group integration example and v9 migration guide references
docs/hooks/useMultipleSelection.mdx	Added deprecation notice recommending useTagGroup and v9 migration guide references
docs/hooks/useCombobox.mdx	Added tag group integration example and v9 migration guide references
docs/hooks/index.mdx	Restructured migration guides section to include v8 and v9

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