[Enhance] Standalone debit/credit note (#14269)

* [Enhance] Standalone debit/credit note

* Test cases

* Test cases and documentation

* Removed credit, debit note links from accounts module

erpnext/controllers/status_updater.py

@@ -159,6 +159,9 @@ class StatusUpdater(Document):
 				if hasattr(d, 'qty') and d.qty < 0 and not self.get('is_return'):
 					frappe.throw(_("For an item {0}, quantity must be positive number").format(d.item_code))
 
+				if hasattr(d, 'qty') and d.qty > 0 and self.get('is_return'):
+					frappe.throw(_("For an item {0}, quantity must be negative number").format(d.item_code))
+
 				if d.doctype == args['source_dt'] and d.get(args["join_field"]):
 					args['name'] = d.get(args['join_field'])