bug(datepicker): input parse validation broken on custom DateAdapter<numeric>

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

Falsy check of value within [datepicker-input-base._isValidValue](https://github.com/angular/components/blob/a1d5614f18066c0c2dc2580c7b5099e8f68a8e74/src/material/datepicker/datepicker-input-base.ts#L382) leads to invalid numeric date values from custom DateAdapter to be treated as valid instead:
```javascript
! 0
// -> true
! NaN
// -> true
```
-> [parseValidator](https://github.com/angular/components/blob/a1d5614f18066c0c2dc2580c7b5099e8f68a8e74/src/material/datepicker/datepicker-input-base.ts#L150) will never return a 'matDatepickerParse' error.

### Reproduction

Steps to reproduce:
1. Use Custom DateAdapter which returns NaN on invalid()
2. Enter invalid characters on the datepicker's input.
3. Leave datepicker

### Expected Behavior

validation error ('format error') shown/raised.

### Actual Behavior

No error validation error ('format error') will be shown/raised.

([datepicker-input-base._isValidValue](https://github.com/angular/components/blob/a1d5614f18066c0c2dc2580c7b5099e8f68a8e74/src/material/datepicker/datepicker-input-base.ts#L382) should check for 'null' | 'undefined' instead of falsy)

### Environment

- Angular: 15.0.4
- CDK/Material: 15.0.4
- Browser(s): Chrome
- Operating System (e.g. Windows, macOS, Ubuntu): Windows

Commencez dans src/material/datepicker/datepicker-input-base.ts, en particulier au niveau de _isValidValue et parseValidator. Reproduisez le problème avec un DateAdapter personnalisé numérique qui renvoie NaN pour une entrée invalide, puis vérifiez que la saisie de caractères invalides et le fait de quitter le datepicker produisent une erreur de validation matDatepickerParse.

Rédigé par le modèle d'indexation à partir du texte de l'issue.