[iOS] Add consistency in date format between platforms

[jsuarezruiz]

Description of Change

Add consistency in date format between platforms.

Issues Resolved

• fixes [Bug] iOS DatePicker only displays the last two digits of the year #13918

API Changes

None

Platforms Affected

• iOS

Behavioral/Visual Changes

None

Before/After Screenshots

Not applicable

Testing Procedure

Launch Core Gallery and navigate to the sample 13918. If can see the century in the DatePicker, the test has passed.

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)

[jsuarezruiz]

In Android we are using the following code:

if (String.IsNullOrWhiteSpace(Element.Format))
{
    EditText.Text = date.ToShortDateString();
}
else if (Element.Format.Contains('/'))
{
    EditText.Text = date.ToString(Element.Format, CultureInfo.InvariantCulture);
}
else
{
    EditText.Text = date.ToString(Element.Format);
}

The default template is "d", and for that reason using NSDateFormatter with Short DateStyle the format is: "MM/dd/yy". In this PR we adapt iOS code to the other platforms.