[FLINK-38863] Fix archunit violations for IndexGeneratorFactory

[shuttie]

https://issues.apache.org/jira/browse/FLINK-38863

This PR fixes the mvn test failing with the error:

[INFO] Running org.apache.flink.architecture.rules.ConnectorRules
[ERROR] Tests run: 1, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 0.029 s <<< FAILURE! - in org.apache.flink.architecture.rules.ConnectorRules
[ERROR] ConnectorRules.CONNECTOR_CLASSES_ONLY_DEPEND_ON_PUBLIC_API  Time elapsed: 0.027 s  <<< FAILURE!
java.lang.AssertionError: 
Architecture Violation [Priority: MEDIUM] - Rule 'Connector production code must depend only on public API when outside of connector packages' was violated (1 times):
Method <org.apache.flink.connector.opensearch.table.IndexGeneratorFactory.createRuntimeIndexGenerator(java.lang.String, [Ljava.lang.String;, [Lorg.apache.flink.table.types.DataType;, 
org.apache.flink.connector.opensearch.table.IndexGeneratorFactory$IndexHelper, java.time.ZoneId)> has parameter of type <[Lorg.apache.flink.table.types.DataType;> in (IndexGeneratorFactory.java:0)
        at com.tngtech.archunit.lang.ArchRule$Assertions.assertNoViolation(ArchRule.java:94)
        at com.tngtech.archunit.lang.ArchRule$Assertions.check(ArchRule.java:86)
        at com.tngtech.archunit.library.freeze.FreezingArchRule.check(FreezingArchRule.java:97)
        at com.tngtech.archunit.junit.internal.ArchUnitTestDescriptor$ArchUnitRuleDescriptor.execute(ArchUnitTestDescriptor.java:166)
        at com.tngtech.archunit.junit.internal.ArchUnitTestDescriptor$ArchUnitRuleDescriptor.execute(ArchUnitTestDescriptor.java:149)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)

Changes:

• As createRuntimeIndexGenerator only needs LogicalType and not DataType, we just change the signature to use non-private class.
• We also removed excessive List <-> Array conversions.

Testing:

• This PR should have no user-visible changes, as we only change signatures of private methods.

Notes:

• A lot of previous archunit violations are now gone, probably due to the upstream Flink fixes.

[boring-cyborg]

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[reta]

Thank you @shuttie !