[FIX] im_livechat: no crash in safari with livechat chatbot

Before this commit, when using a livechat chatbot from visitor
and selecting a chatbot option, there was the following traceback:

```
UncaughtPromiseError > SyntaxError
Uncaught Promise > JSON Parse error: Unterminated string
SyntaxError: JSON Parse error: Unterminated string
parse@[native code]
updateSession
```

This happens because the session cookie had incorrect format for its
content. This was caused by a history prop whose content had the
character "→". When setting the cookie, the stringified object is
only partially inserted until this "→", which made the content
non-JSON parseable as the string is incomplete.

This commit fixes the issue by replacing all occurrences of the
character "→" by a whitespace, so that the setting of the cookie
works and insert the whole stringified object as intended.

Note that this "→" is used for data that is not used in the context
of livechat chatbot for the visitor, therefore this alteration of
the content has functionally no effect.

opw-3527969

closes odoo/odoo#139606

X-original-commit: 64efe60f92679767af769125ce7515ca3fff8c49
Signed-off-by: Matthieu Stockbauer (tsm) <tsm@odoo.com>
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/im_livechat/static/src/embed/common/livechat_service.js

@@ -116,7 +116,7 @@ export class LivechatService {
         });
         cookie.delete(this.SESSION_COOKIE);
         cookie.delete(this.OPERATOR_COOKIE);
-        cookie.set(this.SESSION_COOKIE, JSON.stringify(session), 60 * 60 * 24); // 1 day cookie.
+        cookie.set(this.SESSION_COOKIE, JSON.stringify(session).replaceAll("→", " "), 60 * 60 * 24); // 1 day cookie.
         if (session?.operator_pid) {
             cookie.set(this.OPERATOR_COOKIE, session.operator_pid[0], 7 * 24 * 60 * 60); // 1 week cookie.
         }