[IMP] web: tz cookie: test if already set

This commit adds a test to save the effort of re-setting the tz
cookie when it is already set. We also merge the tz cookie script
with the one defining session_info.

Commit motivated by discussion on PR #55726

closes odoo/odoo#57218

X-original-commit: 0a43d8040f0c5ec8e9728b2e9da8c7d46d7292bb
Signed-off-by: Olivier Dony (odo) <odo@openerp.com>

addons/web/views/webclient_templates.xml

@@ -466,12 +466,6 @@
         <xpath expr="//head/meta[last()]" position="after">
             <meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no"/>
         </xpath>
-        <xpath expr="//head" position="inside">
-            <script type="text/javascript">
-                const userTZ = Intl.DateTimeFormat().resolvedOptions().timeZone;
-                document.cookie = `tz=${userTZ}; path=/`;
-            </script>
-        </xpath>
         <xpath expr="//head/link[last()]" position="after">
             <t t-call-assets="web.assets_common" t-js="false"/>
             <t t-call-assets="web.assets_frontend" t-js="false"/>
@@ -479,6 +473,10 @@
         <xpath expr="//head/script" position="after">
             <script type="text/javascript">
                 odoo.session_info = <t t-raw="json.dumps(request.env['ir.http'].get_frontend_session_info())"/>;
+                if (!/(^|;\s)tz=/.test(document.cookie)) {
+                    const userTZ = Intl.DateTimeFormat().resolvedOptions().timeZone;
+                    document.cookie = `tz=${userTZ}; path=/`;
+                }
             </script>
             <t t-call-assets="web.assets_common_minimal_js" t-css="false" defer_load="True"/>
             <t t-call-assets="web.assets_frontend_minimal_js" t-css="false" defer_load="True"/>