k-table: fix sortable rows

[distantnative]

Description

Summary of changes

• Table sections: Only allow sorting rows that are sortable.
• Previously, the rows itself weren't sortable as the sort handle was hidden, but other sortable rows could be moved above/below/in-between unsortable rows.
• This PR aligns the behavior/code with how it's done for the other layouts (with k-items)

Changelog

Fixes

• Sections with table layout: fixed some issues with sorting rows that should be unsortable

Ready?

• In-code documentation (wherever needed)
• Unit tests for fixed bug/feature
• Tests and CI checks all pass

For review team

• Add lab and/or sandbox examples (wherever helpful)
• Add changes & docs to release notes draft in Notion