fix(setDefaultsOnInsert): run setters on default values during upsert

[mahmoodhamdi]

Problem

When using setDefaultsOnInsert with upsert operations, default values are not passed through setters. This means a schema like:

const schema = new Schema({
  name: String,
  slug: {
    type: String,
    default: 'Hello World!',
    set: function(v) {
      return v.toLowerCase().replace(/[^a-z0-9]+/g, '-').replace(/(^-|-$)/g, '');
    }
  }
});

will store slug as 'Hello World!' when upserted, instead of 'hello-world' (what you get with normal document creation).

Root Cause

In lib/helpers/setDefaultsOnInsert.js, schemaType.getDefault() was called with init = true. This causes _applySetters to skip all setters, since init is meant to signal that the value is being initialized and shouldn't go through setter transformations.

Solution

Changed init from true to false in the getDefault() call so setters run on default values, matching the behavior of normal document creation via new Model().

Also updated the existing test from gh-16025 which was asserting the old (buggy) behavior, and added a unit test in test/helpers/setDefaultsOnInsert.test.js.

How to Test

const schema = new Schema({
  name: String,
  slug: {
    type: String,
    default: 'Hello World!',
    set: v => v.toLowerCase().replace(/[^a-z0-9]+/g, '-').replace(/(^-|-$)/g, '')
  }
});
const Test = mongoose.model('Test', schema);

await Test.updateOne(
  { name: 'test' },
  { $set: { name: 'test' } },
  { upsert: true, setDefaultsOnInsert: true }
);

const doc = await Test.findOne({ name: 'test' });
assert.equal(doc.slug, 'hello-world'); // was 'Hello World!' before this fix

Fixes #16051

[vkarpov15]

LGTM although for caution I'll merge into 9.4. I don't expect this to be backwards breaking because setters already run on non-default values so I think it is reasonable to assume that setters already work on queries.