Wrong field processing order with discriminators

[piyushk96]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

7.4.5

Node.js version

16

MongoDB server version

N/A

Typescript version (if applicable)

N/A

Description

When using discriminator sub schema fields are processed before the base schema fields but according to mongoose documentation the fields should be processed in order of their definition in schema.

In my use case, I need to set and validate values of the sub schema fields according to a field of base schema. But since sub schema fields are processed first the base schema fields are coming to be undefined in sub schema field's setters and validators.

Steps to Reproduce

const mongoose = require('mongoose');
const { Schema } = mongoose;

mongoose.connect('mongodb://localhost:27017/testdb');

const E1 = new Schema({
  f1: {
    type: Number,
    set() {
      console.log('Set 1');
      return 1;
    },
    validate: [
      {
        validator: (v) => {
          console.log('Validator 1');
          return true;
        }
      }
    ]
  },

});
const E1Model = mongoose.model('E1', E1);

const E2 = new Schema({
  f2: {
    type: Number,
    set() {
      console.log('Set 2');
      return 2;
    },
    validate: [
      {
        validator: (v) => {
          console.log('Validator 2');
          return true;
        }
      }
    ]
  },
});
const E2Model = E1Model.discriminator('E2', E2, { discriminatorKey: 'kind' })

async function main() {
  let item1 = new E2Model({ f1: 1, f2: 2 });
  item1 = await item1.save()
}

main();

Expected Behavior

The setters & validators of base class fields should be processed before sub class fields