Fix caret jumping to wrong position when decorations restructure DOM #5987

[dannelundqvist]

Description

When decorate changes asynchronously, the caret jumps to the wrong position.

Root cause: Text components re-render in a separate React commit from Editable. When decorations restructure the DOM, Editable's selection-restoration useLayoutEffect has already run and never re-fires, leaving the browser selection pointing at a stale node.

A forceUpdate() in useDecorateContext forces Editable to re-render in the same commit as the Text components, so the layout effect runs after the updated DOM is in place.

Example and integration test added: Decorations Async — an editor where duplicate words are highlighted 600 ms after each edit, demonstrating that the caret stays put when the async decoration update fires.

Closes #5987

Checks

• [x ] The new code matches the existing patterns and styles.
• [ x] The tests pass with yarn test.
• [ x] The linter passes with yarn lint. (Fix errors with yarn fix.)
• [ x] The relevant examples still work. (Run examples with yarn start.)
• [x ] You've added a changeset if changing functionality. (Add one with yarn changeset add.)

[changeset-bot]

🦋 Changeset detected

Latest commit: 072cd7b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
slate-react	Patch

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