Adds `acceptEmptyDate` property to `InputDatePickerFormField`.

Fixes: #117511

| `acceptEmptyDate` is **false** | `acceptEmptyDate` is **true** |
| --- | ---|
| ![acceptemptydate_false](https://user-images.githubusercontent.com/13456345/229893658-280ecdee-d509-4579-b53c-9d8d485c61b4.gif) | ![acceptemptydate__true](https://user-images.githubusercontent.com/13456345/229895144-115e71bd-e5bb-4653-8db2-9f57dd8262aa.gif) |