feat(react-swatch-picker): expose headless base APIs

[Dmytro Kirpa (dmytrokirpa)]

Motivation

Extract reusable unstyled state from the SwatchPicker family so headless consumers can compose the existing interaction and accessibility behavior without Fluent styling concerns.

Changes

• add base props and state types for the SwatchPicker component family
• split public hooks into base state and styled composition layers
• update render functions and exports to consume base state
• preserve existing focus, context, selection, and ImageSwatch precedence behavior
• update API output and add a package change file

Review guidance

Review this PR relative to test/react-swatch-picker-hooks. The tests in #36533 establish the behavior preserved by the extraction.

Validation

• yarn nx run-many -t test type-check lint -p react-swatch-picker --nxBail

PR stack

1. test(react-swatch-picker): add hook state coverage #36533
2. This PR: expose reusable SwatchPicker base APIs
3. feat(react-headless-components-preview): add swatch picker controls #36535

Depends on #36533 and should be merged second.

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