[IMP] web: allow js_class in FormViewDialog

This commit allows custom classes (js_class) to be used in FormViewDialog.

task-2685472

Part-of: odoo/odoo#79654

addons/web/static/src/legacy/js/views/view_dialogs.js

@@ -191,7 +191,6 @@ var FormViewDialog = ViewDialog.extend({
     open: function () {
         var self = this;
         var _super = this._super.bind(this);
-        var FormView = view_registry.get('form');
         var fields_view_def;
         if (this.options.fields_view) {
             fields_view_def = Promise.resolve(this.options.fields_view);
@@ -203,6 +202,9 @@ var FormViewDialog = ViewDialog.extend({
             var refinedContext = _.pick(self.context, function (value, key) {
                 return key.indexOf('_view_ref') === -1;
             });
+            var xml = new DOMParser().parseFromString(viewInfo.arch, "text/xml")
+            var key = xml.documentElement.getAttribute("js_class");
+            var FormView = view_registry.get(key || 'form');
             var formview = new FormView(viewInfo, {
                 modelName: self.res_model,
                 context: refinedContext,