[FIX] point_of_sale: env.isMobile not defined at startup

Before this commit, env.isMobile was defined lately and
you have to wait the next update of the template.

Steps to reproduce:
- Open "bar" POS session
=> 'pos-branding' is present in the header bar

X-original-commit: 931304b9e7085c77e5b9bed8054ae47fc2a6168f
Part-of: odoo/odoo#79448

addons/point_of_sale/static/src/js/chrome_adapter.js

@@ -28,6 +28,8 @@ export class ChromeAdapter extends Component {
 
         this.env = owl.Component.env;
         useBus(this.env.qweb, "update", () => this.render());
+        setupResponsivePlugin(this.env);
+
         const chrome = owl.hooks.useRef("chrome");
         owl.hooks.onMounted(async () => {
             // Add the pos error handler when the chrome component is available.
@@ -47,7 +49,6 @@ export class ChromeAdapter extends Component {
             configureGui({ component: chrome.comp });
             await chrome.comp.start();
             registry.category("main_components").add("BlockUI", BlockUiFromRegistry);
-            setupResponsivePlugin(this.env);
         });
     }
 }