Issue #3608101: Render multi-value entity reference props as individual rows

Switch array props from the tags widget (single comma-separated input) to a new per-delta widget entity_reference_autocomplete_multi. Canvas's DrupalInputMultivalueForm renders each value as an individual row with a remove button and an + Add row at the bottom, matching the standard multi-value field UX for all other field types.

A separate widget plugin ID is required so hook_field_widget_info_alter() can register a different Canvas transform chain: entityReferenceAutocomplete without firstRecord or mainProperty, returning the full array of {target_id: N} records for Canvas StaticPropSource to resolve.

The tags widget (entity_reference_autocomplete_tags) remains available as an explicit opt-in via x-entity-widget for component authors who prefer the single-input approach.