fix: add support for implements within classes

[yradchen]

Add support for implements within classes. Currently if implementing an interface it becomes a mixin which isn't accurate. When TypeScript implements an interface it should remain an "implements".

Please double check the change to namespaces.spec.ts.snap this is the only one I'm iffy about but I believe it was wrong originally

References issue

[orta]

Cool, this looks reasonable to me - I'm not too deep on how the flow syntax looks/feels but it eyeballs well to me (and didn't really exist prior) 👍🏻