Add a didFailProvisionalNavigation observer.

[keisukeYamagishi]

Overview

I am encountering a significant issue as didFailProvisionalNavigation is missing in WKWebView+Rx.

For more details on this function, please refer to the Apple Developer documentation:

webView(_:didFailProvisionalNavigation:withError:)

https://developer.apple.com/documentation/webkit/wknavigationdelegate/1455637-webview

I have added this function and would greatly appreciate it if knowledgeable individuals could review it.

Thank you very much in advance for your assistance.

[freak4pc]

Hey there! I appreciate the addition, but we generally don't want to add more 'bloat' and code for very narrow and specific use cases that aren't very widely asked by the community. This is true for this PR and also #2619, so i'll close them.

If the use case exists for your, I suggest extending locally for your codebase.

Thanks!