fix(schematype): consistently set wasPopulated to object with value property rather than boolean

Re: #14418
Re: #6048

Author: vkarpov15

lib/schematype.js

@@ -1505,7 +1505,7 @@ SchemaType.prototype._castRef = function _castRef(value, doc, init) {
   }
 
   if (value.$__ != null) {
-    value.$__.wasPopulated = value.$__.wasPopulated || true;
+    value.$__.wasPopulated = value.$__.wasPopulated || { value: value._id };
     return value;
   }
 
@@ -1531,7 +1531,7 @@ SchemaType.prototype._castRef = function _castRef(value, doc, init) {
     !doc.$__.populated[path].options.options ||
     !doc.$__.populated[path].options.options.lean) {
     ret = new pop.options[populateModelSymbol](value);
-    ret.$__.wasPopulated = true;
+    ret.$__.wasPopulated = { value: ret._id };
   }
 
   return ret;