[FW][FIX] website: make multirange widget works with sr@latin lang code

The range widget doesn't work with Serbian language, because language
locale subtag contains `@`.

Steps to reproduce:
1. Activate Serbian Latin language (sr@latin) on your website
2. Go to /shop
3. Switch to Serbian lang

The price ranger slider (which can be disabled) will throw this TB:
"RangeError: Incorrect locale information provided".

The fix is to do as other places in the code: replace this specific
lang code with the expected one.
Ideally, a util method should be used at all those places.

closes odoo/odoo#148593

Forward-port-of: odoo/odoo#148279
Signed-off-by: Romain Derie (rde) <rde@odoo.com>

addons/website/static/lib/multirange/multirange_custom.js

@@ -264,7 +264,8 @@ export class Multirange {
     }
 
     formatNumber(number) {
-        const locale = document.querySelector("html").getAttribute("lang");
+        const language = document.querySelector("html").getAttribute("lang");
+        const locale = language === "sr@latin" ? "sr-Latn-RS" : language.replace(/_/g, "-");
         let formatedNumber = number.toLocaleString(locale, {
             minimumFractionDigits: 2,
             maximumFractionDigits: 2,