Adds tests for Schema 4.5 and modifies existing tests as needed

Purpose

This PR adds tests for Schema 4.5 and Schema 4.5 features while adjusting existing tests as-needed.

closes: datacite/datacite#1932

Approach

I copied over the existing 4.4 tests to a spec/kernel-4.5 folder. The tests in spec/kernel-4.5 and spec/kernel-4 are identical, per previous patterns. The XML examples that had been removed in a cleanup were restored to ensure that tests that relied on these files would continue to pass.

Because the kernel-4 XML examples had changed, some tests for earlier versions were changed to target specific schema version examples.

Tests for 4.5 features were added to spec/kernel-4.5/other_spec.rb, spec/kernel-4/other_spec.rb, spec/kernel-4.5/example_relation_type_collects_is_collected_by_spec.rb, and spec/kernel-4/example_relation_type_collects_is_collected_by_spec.rb

Open Questions and Pre-Merge TODOs

Learning

Types of changes

[ ] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)

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Be humble in the language and feedback you give, ask don't tell.
Consider using positive language as opposed to neutral when offering feedback. This is to avoid the negative bias that can occur with neutral language appearing negative.
Offer suggestions on how to improve code e.g. simplification or expanding clarity.
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datacite / schema