_dateToDataValue() should not use formatted month and date

[hkvstore]

Prerequisites

• I have searched for duplicate or closed issues.
• I have validated my setup against the latest version on StackBlitz.
• I have read the contributing guidelines.

Describe the issue

Currently the code is:

  private _dateToDataValue(date: DateTime): string {
    if (!DateTime.isValid(date)) return '';

    return `${date.year}-${date.monthFormatted}-${date.dateFormatted}`;
  }

If Arabic locale is used, the outputted HTML will be like:

But the date value should not be formatted.

StackBlitz fork

https://stackblitz.com/edit/tempus-dominus-v6-simple-setup-hyrhpd?file=index.js

What operating system(s) are you seeing the problem on?

Windows

What browser(s) are you seeing the problem on?

Chrome

What version of are you using? You can find this information from the sample StackBlitz.

6.7.19

What your browser's locale? You can find this information from the sample StackBlitz.

en-US

[Eonasdan]

this is done in 6.9.4