Returns all field names referenced within a
PopupTemplate's
content. If the content is a function or Promise, it should be evaluated
first. Field names of FieldInfos are not returned.
Parameters
template: PopupTemplateProperties | PopupTemplate
The PopupTemplate from which the field names are extracted.
Returns all field names referenced within a PopupTemplate's content. If the content is a function or Promise, it should be evaluated first. Field names of FieldInfos are not returned.