minor symfony#20430 [Form] Allow integer for the calendar option of DateType (MrYamous)

This PR was merged into the 7.2 branch.

Discussion
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[Form] Allow integer for the calendar option of `DateType`

Completes symfony#20145 after [code PR](symfony/symfony#59014)

Commits
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2083dc2 Allow integer for the calendar option of DateType

Author: javiereguiluz

reference/forms/types/date.rst

@@ -156,11 +156,12 @@ values for the year, month and day fields::
 ``calendar``
 ~~~~~~~~~~~~
 
-**type**: ``\IntlCalendar`` **default**: ``null``
+**type**: ``integer`` or ``\IntlCalendar`` **default**: ``null``
 
 The calendar to use for formatting and parsing the date. The value should be
-an instance of the :phpclass:`IntlCalendar` to use. By default, the Gregorian
-calendar with the application default locale is used.
+an ``integer`` from :phpclass:`IntlDateFormatter` calendar constants or an instance
+of the :phpclass:`IntlCalendar` to use. By default, the Gregorian calendar
+with the application default locale is used.
 
 .. versionadded:: 7.2