Handle numbers and booleans in slate-hyperscript

[12joan]

Description
Previously, trying to include a number or boolean as a child in slate-hyperscript resulted in an error like Error: Unexpected hyperscript child object: <value>.

This PR updates the child handling logic to make number and boolean handling consistent with React JSX. Numbers are converted to strings, and booleans are ignored.

Example

<element>{4}</element> // Element containing { text: '4' }
<element>{true}{false}</element> // Empty element, since true and false are ignored

Context
Since JSX is not type-safe, it's quite common to accidentally pass a number instead of a string as a child of a JSX tag when creating JSX dynamically.

Ignoring booleans lets us safely use patterns like {condition && <element />}.

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: e474d91

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

This PR includes changesets to release 1 package

Name	Type
slate-hyperscript	Patch

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Click here if you're a maintainer who wants to add another changeset to this PR

[12joan]

From yarn fix

[12joan]

From yarn fix