[FIX] web: allow the usage of .at in lower versions of Safari

Commit [1] refactored the mail code and introduced a few .at called on
Array typed objects. This is not supported in lower versions of iOS
which some of our users and visitors still use as shown by [2].

This commit introduces a polyfill to support the feature on Safari
<=15.3.

[1]: https://github.com/odoo/odoo/commit/631ae1c4d865b912a59ddc8a068bdbf2dedd6a04
[2]: https://github.com/odoo/odoo/issues/142022

opw-3824593

closes odoo/odoo#160758

Signed-off-by: Romain Derie (rde) <rde@odoo.com>

addons/web/__manifest__.py

@@ -124,6 +124,7 @@ This module provides the core of the Odoo Web Client.
         ],
         'web.assets_frontend_minimal': [
             'web/static/src/polyfills/object.js',
+            'web/static/src/polyfills/array.js',
             'web/static/src/module_loader.js',
             'web/static/src/session.js',
             'web/static/src/core/browser/cookie.js',

addons/web/static/src/polyfills/array.js

@@ -0,0 +1,8 @@
+if (!Array.prototype.at) {
+    Array.prototype.at = function (index) {
+        if (index >= 0) {
+            return this[index];
+        }
+        return this[this.length + index];
+    };
+}