Realtime editor broken for older browsers

Hi Benjamin Fischer,

Thank you for testing the latest version of XWiki and for taking the time to debug and create a PR for the issue you are facing. Regarding this issue:

• our Browser Support Strategy emphasizes that we support only the latest stable versions of Edge, Firefox, Chrome, Safari.
• Promise.try() is supported by all of these, based on https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/try#browser_compatibility . Moreover, this API is marked as "Baseline":

  Since January 2025, this feature works across the latest devices and browser versions.

• our Browser Support Strategy doesn't mention anything about Firefox ESR https://www.mozilla.org/en-US/firefox/enterprise/ (Extended Support Release), which implies it's not supported (meaning that we don't test XWiki with this Firefox version neither manually nor automated).
• Even if we merge your PR, without proper testing (automated preferably), we can't prevent or catch the usage of such APIs in the future
• It adds a bit to the technical dept of the project (we need to remember to switch back to Promise.try() when Firefox ESR add support for it, which may happen very soon).

Based on this I think we should close this issue (and its PR) as Won't Fix.