Set value on focus out and changed signal for datetime widget

The focus out of child widgets must call focus out method.
And we need to connect to the datetime-changed event as DateTime does not call
the __init__ method of Date.

Closes #12020
(grafted from 62934f0e75525d65719bcc83f750d5e9070e4632)

--HG--
branch : 6.0

tryton/tryton/gui/window/view_form/view/form_gtk/calendar_.py

@@ -135,6 +135,8 @@ class DateTime(Date):
             child.connect('key_press_event', self.sig_key_press)
             child.connect('activate', self.sig_activate)
             child.connect('changed', lambda _: self.send_modified())
+            child.connect('focus-out-event', lambda *a: self._focus_out())
+        self.entry.connect(self._changed_signal, self.changed)
         self.widget.pack_start(self.entry, expand=False, fill=False, padding=0)
 
     @classmethod