Issue #3276088 Allow autofill from any source entity.

This adds a new submission configuration option for autofilling submissions with a previous submission. Instead of restricting previous submission data that which came from the same source entity, this option allows Webform to pull data from the same webform (and user), but from any source entity. An example use case would be to have different source nodes for each "thing" (month, item, location) but still want to prefill data for the user from another month, item or location node.