feat(react-label): add useLabelBase_unstable hook

[dmytrokirpa]

Summary

• Adds LabelBaseProps type derived from LabelProps by omitting design props (size, weight)
• Adds LabelBaseState type derived from LabelState by omitting the same design props
• Adds useLabelBase_unstable hook that handles pure slot structure logic (root, required, disabled) without design-specific concerns
• Refactors useLabel_unstable to call useLabelBase_unstable and spread its results, then add design props
• Updates renderLabel_unstable to accept LabelBaseState instead of LabelState
• Exports new types and hook from the package public index

Tracking: #35562

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