Now that we have a NetworkError enum with more granularity, we can use the failure type to decide whether it's useful to retry an EventSource connection. Let's add a is_permanent_failure method is NetworkError which includes:

• InvalidPort
• MixedContent
• ContentSecurityPolicy
• UnsupportedScheme

Then we can call this from the EventSource code instead of the current match against the url's scheme. This is tested by ./mach test-wpt tests/wpt/tests/eventsource.