UseWatch with an input field that has a default value returns undefined when the input field is not changed

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**What you were expecting:**
I would expect that useWatch returns the default value of the field.

**What happened instead:**
useWatch returns undefined, untill I change the watched field.

**Steps to reproduce:**

create a form with an input that has a default value, then have another component use useWatch on that input field, the resulting value is undefined untill you change the input.

**Related code:**
I created a WatchBug component in the PostCreate file. It watches the Published at input. you see that initally the value returned is undefined.
https://stackblitz.com/edit/github-mjvobu?file=src%2Fposts%2FPostCreate.tsx

**Environment**

* React-admin version: 4.15.2
* Last version that did not exhibit the issue (if applicable): 4.8.4 does not show the bug, I did not try other versions inbetween.

Working version on 4.8.4
https://stackblitz.com/edit/github-ladv9x?file=src%2Fposts%2FPostCreate.tsx

Start with the WatchBug component in src/posts/PostCreate.tsx from the linked StackBlitz and inspect how useWatch observes the Published at input. Reproduce the behavior on react-admin 4.15.2 and compare it with 4.8.4; done means useWatch returns the field's default value before the input changes.

Written by the indexing model from the issue text.