Add Context Action (Alt+Enter) to ignore lints

[feinstein]

If I get a lint warning, and I hit Alt+Enter, I don't get any smart actions to ignore the warning... but if I go to the Dart Analysis tab, I get the shortcuts there:

IIRC from my old times of Java, we had a smart action on Alt+Enter to ignore warnings, and since this is already there in the Dart Analysis tab, I wonder if this is just a quick adjustment to make it work

[pq]

Nice idea. Since this would be implemented in the Dart Plugin, moving it there.