update assign_prov_state to include BCRs and confirm that province_state aligns with prov_state

[AdamCSmithCWS]

This function should be generalised to be any sf map (not just provinces and states).

Also: in the current application, the function sometimes assigns strata (e.g., latlong grid cells) to prov_state values that differ from province_state values. e.g., prov_state == "AK" & province_state == "BC".