chore: fix formiojs tests

[brendanbond]

Link to Jira Ticket

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Description

Since Day components emptyValue was changed to an empty string, validation is broken. This PR changes the isPartialDay method to return true on an empty value.

Additionally, some type guards were changed to handle undefined components.

Breaking Changes / Backwards Compatibility

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Dependencies

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How has this PR been tested?

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Checklist:

• I have completed the above PR template
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new warnings
• My changes include tests that prove my fix is effective (or that my feature works as intended)
• New and existing unit/integration tests pass locally with my changes
• Any dependent changes have corresponding PRs that are listed above