ui-core: enable the user to type in the date picker

[clarani]

closes #526

Some remarks:

• when the user clicks on the input, the calendar is not opened automatically anymore
• if the user types a string which is not a date, the date value is not updated
• if the user types a valid string but the date is not in the selectable slot, then an error is displayed (the invalid date is not updated in the parent component)
• if the calendar is opened and the user enters a valid date, then the calendar view is correctly updated
• if an invalid date is entered and the user picks a date from the calendar, then the error is not displayed anymore

Technical remarks:

• I moved the selectableSlot props so it is more easier to access it

When the input is invalid:

[clarani]

Thanks for your review, I modified a bit the behaviors:

• if the user enters a string which does not contain only slashes and numbers, then an error is displayed (example toto)
• if the user enters a string which contains only slashes and numbers but which is longer than 8 characters, then an error is displayed (for instance 01/01/2024)