[RHCLOUD-48734] Add traditional expandable row support to DataViewTable

[katarinazaprazna]

Summary

• Add support for traditional expandable rows
• Traditional expand renders a dedicated toggle column as the first column
• No breaking API changes: columnId on ExpandableContent changed from required to optional, existing consumers with columnId get identical compound behavior
• Add examples and documentation for both expand types

Test plan

• npm run test passes (11 tests in DataViewTableBasic)
• Docs dev server: expandable rows example renders with toggle column
• Docs dev server: compound expandable rows example renders unchanged
• Traditional expand: rows without content show empty toggle cell

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Closes RHCLOUD-48734

Assisted-by: Claude Code