Improve ColumnarRow

[pettyjamesm]

Extracted partially from trinodb/trino#9916

• Adds ColumnarRow#mayHaveNull() and uses it inside of hive's StructCoercer
• Removes an unnecessary field array copy, all usage sites are private to the class and do not require a defensive clone
• Adds special case for creating ColumnarRow instances from DictionaryBlocks that have no nulls

== NO RELEASE NOTE ==

[mbasmanova]

@jamesgpearce Looks good to me. Have you observed some measurable performance wins? Do you know if the changes are fully covered by existing tests?

[pettyjamesm]

Have you observed some measurable performance wins?

This is pending collection from our testing environment. I suspect it's a modest improvement, mostly from its usage in SpillableFinalOnlyGroupedAccumulator and from specific narrow usage scenarios involving the hive struct coercer.

Do you know if the changes are fully covered by existing tests?

Yeah, the existing TestColumnarRow covers RLE / Dictionary / plain block combinations with and without null rows exhaustively.

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. If you'd still like this PR merged, please comment on the task, make sure you've addressed reviewer comments, and rebase on the latest master. Thank you for your contributions!