[FIX] web: keep picker and component date in sync

When changing the value of a DateField outside of the datepicker, the dates
kept by the datepicker instance and the DateField component will get out of
sync. This can happen, for example, when clicking the new button when in a form
view containing such a field. The component is kept, but the date is changed
(generally set to false in this case) while the state of the datepicker stays
the same.

As a result, when clicking the selected date in the datepicker, no change event
is triggered making it impossible to select. This can be frustrating when
manually inputting a series of documents with the same dates.

opw-3459123

closes odoo/odoo#134911

Signed-off-by: Julien Mougenot (jum) <jum@odoo.com>