Add support for crt.CanDiscardUnsavedDataRequest in the mobile app

I already raised this issue here: https://community.creatio.com/questions/creatio-mobile-discard-unsaved-…

On web, I can handle crt.CanDiscardUnsavedDataRequest to control when the "discard unsaved changes" popup appears. On mobile, this option doesn't exist, even though the same business logic often needs to work on both platforms. I understand the popup protects users from losing data by accident, and I'm not asking to remove that protection by default. I just want the option to override it when I decide it's needed, the same way I already can on web.

I know this wouldn't cover system-level gestures or hardware back buttons, since those happen outside the JS layer. That's also true on web (closing the tab isn't covered either), but the handler is still useful for everything that goes through crt.ClosePageRequest and similar in-app navigation. Adding this would bring mobile closer to feature parity with web, giving developers the same control they already have, without changing default behavior for users who don't need it.