[IMP] web: state_selection widget readonly if field readonly

The current implementation of the state_selection widget always makes it
editable even if the field is readonly.

We improved this behavior by removing the handle of click on the widget
when the field is readonly, but keeping it even if the view is not in
edit mode, because it used for example in project to change state even
when view is not editable.

closes odoo/odoo#29218

addons/web/static/src/js/fields/basic_fields.js

@@ -1960,11 +1960,10 @@ var StateSelectionWidget = AbstractField.extend({
      * @override
      */
     _render: function () {
-        var self = this;
         var states = this._prepareDropdownValues();
         // Adapt "FormSelection"
         // Like priority, default on the first possible value if no value is given.
-        var currentState = _.findWhere(states, {name: self.value}) || states[0];
+        var currentState = _.findWhere(states, {name: this.value}) || states[0];
         this.$('.o_status')
             .removeClass('o_status_red o_status_green')
             .addClass(currentState.state_class)
@@ -1979,6 +1978,10 @@ var StateSelectionWidget = AbstractField.extend({
         var $dropdown = this.$('.dropdown-menu');
         $dropdown.children().remove(); // remove old items
         $items.appendTo($dropdown);
+
+        // Disable edition if the field is readonly
+        var isReadonly = this.record.evalModifiers(this.attrs.modifiers).readonly;
+        this.$('a[data-toggle=dropdown]').toggleClass('disabled', isReadonly || false);
     },
 
     //--------------------------------------------------------------------------