[pickers] Remove TDate generics in favor of PickerValidDate direct usage

[flaviendelangle]

Closes #14796

Side note: all PickerValidDate | null passed as a generic will be replaced with a true or false once TValue is replaced by TIsRange (phrase 2 of #14823).

I will do the migration guide after the phase 2 of #14823 to have a finalized list of the breaking changes on the generics.

Changelog

Pickers

• The TDate generic has been removed from all the types, interfaces, and variables of the @mui/x-date-pickers and @mui/x-date-pickers-pro packages.

  If you were passing your date object type as a generic to any element of one of those packages, you can remove it:

  -<DatePicker<Dayjs> value={value} onChange={onChange} />
  +<DatePicker value={value} onChange={onChange} />
  
  -type Slot = DateCalendarSlots<Dayjs>['calendarHeader'];
  +type Slot = DateCalendarSlots['calendarHeader'];
  
  -type Props = DatePickerToolbarProps<Dayjs>;
  +type Props = DatePickerToolbarProps;

  A follow-up release will add the full list of the impacted elements to the migration guide.

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[flaviendelangle]

@LukasTy one option would be to add the following code in one of the doc files:

declare module '@mui/x-date-pickers/models' {
  interface PickerValidDateLookup {
    fakeDocAdapter: any;
  }
}

It would not impact Codesandbox / Stackblitz.
We would have any as a value in the doc examples but I don't think we care since today we have the union of all the date library types and we never really missed this type safety.

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[github-actions]

This pull request has conflicts, please resolve those before we can evaluate the pull request.

[LukasTy]

Epic work! 💯 🚀 🌔
Massive piece of destruction and cleanup. 👏

Leaving some non-blocking comments. 😉