Handle "Unsupported notification method: $/analyzerStatus"

[jonas-jonas]

The Dart analysis server uses $/analyzerStatus to indicate the status of the analyzer.
LSP4J does not support this, and throws an error to the console. We should suppress or handle the error accordingly.

Note: that it might be useful to actually have the notification be used for an indicator in the ui (maybe a progress bar at the bottom).

[jonas-jonas]

I pushed a fix to 2f87ec3 that should handle this. Also opens up the possibility to handle other such customs methods (very easily).

Will have to check how to present the user with the analyzing indicator.

[jonas-jonas]

Fixed via 2ced7b7