[FIX] web: extract date picker's input setter

This commit extracts the DatePicker widget's input setter to allow
overriding it and preventing from calling the `datetimepicker` lib when
not initialized (like on mobile).

Note: this change will be used on enterprise.

opw-2242880

X-original-commit: c0413868a8728500c52b7e1dd9a0035f90b654fd

addons/web/static/src/js/widgets/date_picker.js

@@ -183,9 +183,7 @@ var DateWidget = Widget.extend({
         this.set({'value': value});
         var formatted_value = value ? this._formatClient(value) : null;
         this.$input.val(formatted_value);
-        this.__libInput++;
-        this.$el.datetimepicker('date', value || null);
-        this.__libInput--;
+        this._setLibInputValue(value);
     },
 
     //--------------------------------------------------------------------------
@@ -231,6 +229,15 @@ var DateWidget = Widget.extend({
     _parseClient: function (v) {
         return field_utils.parse[this.type_of_date](v, null, {timezone: false});
     },
+    /**
+     * @private
+     * @param {Moment|false} value
+     */
+    _setLibInputValue: function (value) {
+        this.__libInput++;
+        this.$el.datetimepicker('date', value || null);
+        this.__libInput--;
+    },
     /**
      * @private
      * @param {boolean} readonly