GH-43170: [Swift] Add StructArray support to ArrowWriter

[abandy]

Rationale for this change

Support for Struct type has been added to the Swift ArrayReader. This change adds this support to the ArrowWriter.

What changes are included in this PR?

Updates to the ArrowWriter to support the Struct type.

Are these changes tested?

Yes, test included in PR

• GitHub Issue: [Swift] Add StructArray support to ArrowWriter #43170

[github-actions]

⚠️ GitHub issue #43170 has been automatically assigned in GitHub to PR creator.

[kou]

+1

[kou]

childrenOffset?

[kou]

@abandy Sorry. I forgot this PR.

Could you rebase on main? Let's merge this before we move swift/ to apache/arrow-swift.

Cc: @raulcd

[raulcd]

Thanks for the ping @kou

[kou]

+1

[kou]

Suggested change

	switch arrowType.id {
	switch typeId {

[kou]

@raulcd We're ready to move swift/!

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 4 benchmarking runs that have been run so far on merge-commit b5b6707.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 22 possible false positives for unstable benchmarks that are known to sometimes produce them.