Breadcrumbs: theme data reference

Reading the data tables. Presence varies by page and state; this is not a requirement to populate every field.

Field	Type	Meaning	Availability
viewModel.breadcrumbs	array	Prepared breadcrumbs collection; may be empty.	When the parent is provided; check optional fields.
viewModel.breadcrumbs[].isCurrent	boolean	Whether current applies; use for display only.	For each existing item; optional child fields depend on item type.
viewModel.breadcrumbs[].label	string	Label value supplied for this context.	For each existing item; optional child fields depend on item type.
viewModel.breadcrumbs[].url	string	Prepared url URL; use unchanged.	For each existing item; optional child fields depend on item type.