feat(ui-react-native): Add theming for Divider primitive

[joebuono]

Description of changes

• Adds theming
• Updates unit tests

Issue #, if available

Description of how you validated changes

Ran in iOS and Android.

Checklist

• PR description included
• yarn test passes
• Tests are updated

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[changeset-bot]

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Latest commit: 7bc5efd

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