Fix: Calling ReactEditor.focus doesn't update useFocused when running in @testing-library/react

[12joan]

Description
Sometimes, when calling ReactEditor.focus in @testing-library/react, the value of useFocused doesn't get updated. This PR addresses this issue by setting IS_FOCUSED to true prior to dispatching a DOM focus event.

Context
The isFocused state variable controlling useFocused (via FocusedContext) is updated in slate.tsx in response to focus and blur events, but the value of isFocused is always pulled from IS_FOCUSED, regardless of which event triggered the update. This stopped working in #5527 when the ReactEditor.focus line setting IS_FOCUSED was moved to after el.focus({ preventScroll: true }).

When running in a real browser, IS_FOCUSED is already set to true when domSelection?.addRange(domRange) is called higher up in ReactEditor.focus, via onDOMSelectionChange.

Checks

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

[changeset-bot]

🦋 Changeset detected

Latest commit: 6076d44

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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