PowerPlant.isPartOf should be object prop (PublicUtility) not string

[VladimirAlexiev]

This PowerPlant https://www.datacommons.org/browser/eia/pp/2322 has link isPartOf being string "eia/u/13407",
rather than a thing: the corresponding PublicUtility https://www.datacommons.org/browser/eia/u/13407 .
Consequently, the section "In Arcs" of the utility doesn't show its power plants.

Maybe the bug is at https://github.com/datacommonsorg/data/blob/master/scripts/us_eia/eia_860/2_plant.tmcf#L12 .
It calls a function isPartOf: C:EIA_860_Schedule_2->UtilityDcid
but it seems to me the output is formatted like a string (just like the prev line eiaPlantCode: C:EIA_860_Schedule_2->PlantCode) ?

[VladimirAlexiev]

Note: https://datacommons.rff.org uses worse IDs (GUIDs instead of EIA ids), but doesn't have this problem:
https://datacommons.rff.org/browser/dc/05gsw4m93mz6 (utility) links to
https://datacommons.rff.org/browser/dc/3lwrcytjq2k09 (power plant).