[FIX] web: char_domain widget re-renders on model change

Before this revision, the `char_domain` re-rendered its display
only when its domain value was changed.

It must re-render as well when the model on which this domain
is applied is changed, as the number of records can
obviously be different.

e.g., in mass-mailing, when changing the recipients type
from partners to leads, the domain doesn't change, it
stays `['opt_out', '=', False]`, but the model on which
this domain is applied does change, as well as the number
of selected records.

opw-658391

addons/web/static/src/js/view_form.js

@@ -2566,6 +2566,15 @@ instance.web.form.FieldCharDomain = instance.web.form.AbstractField.extend(insta
         this.on("change:effective_readonly", this, function () {
             this.display_field();
         });
+        if (this.options.model_field){
+            this.field_manager.fields[this.options.model_field].on("change:value", this, function(){
+                if (self.view && self.view.onchanges_mutex){
+                    self.view.onchanges_mutex.def.then(function(){
+                        self.display_field();
+                    });
+                }
+            });
+        }
         this.display_field();
         return this._super();
     },