fix(model): ensure consistent ordering of validation errors in insertMany() with ordered: false and rawResult: true

[vkarpov15]

Re: #12791

Summary

#12791 points out a few issues with our error reporting with create() and insertMany(). We do have a workaround using insertMany(), but the workaround does have a potential flaw: currently, res.mongoose.validationErrors can report validation errors in any order.

Specifically, the validation errors are in the order that the errors occur, not in the order of the original documents passed in. So if doc1 and doc2 both fail validation, const res = await Model.insertMany([doc1, doc2], { ordered: false, rawResult: true }) can end up with doc2's validation error before doc1's in res.mongoose.validationErrors if doc1's validation takes longer than doc2's.

With this change, res.mongoose.validationErrors will always be in the same order as the documents passed in. So doc1's validation error will always be before doc2's. So to check whether a document at index i was actually inserted, you need to check if i in res.insertedIds. To check if there was a MongoDB-specific write error, check if !(i in res.insertedIds)

Examples

[hasezoey]

LGTM