[Variant] Move ArrayVariantToArrowRowBuilder to variant_to_arrow

[liamzwbao]

Which issue does this PR close?

• Part of [Variant] Support Shredded Lists/Array in variant_get #8082.

Rationale for this change

To support Lists/Array in variant_get, it's better to move ArrayVariantToArrowRowBuilder from shred_variant to variant_to_arrow and be shared with variant_get. In the meantime, some code movement in variant_to_arrow would help to get a better overview of the overall implementation

What changes are included in this PR?

This PR can be reviewed commit by commit:

• Move VariantToArrowRowBuilder and related impl to the top of variant_to_arrow
• Push the FixedSizeList check from make_variant_to_shredded_variant_arrow_row_builder down to ArrayVariantToArrowRowBuilder
• Move ArrayVariantToArrowRowBuilder to variant_to_arrow

Are these changes tested?

Covered by existing tests

Are there any user-facing changes?

No

[liamzwbao]

Hi @alamb @scovich, here is the PR with code movement only. Once it's merged, #9049 would be easier to review

[klion26]

Thanks for the contribution, LGTM

[alamb]

Thanks @liamzwbao and @klion26

[scovich]

Sorry I missed the notification, but this looks great, thanks!