Clean up code actions code

[davidwengier]

This PR is a style-only clean up of our code actions handlers and related code. Definitely could have gone further (more collection pooling, returning concrete types etc.) but I wanted to try to have it serve as an indication for what we consider our current idiomatic coding style* and to avoid conflicts with the extract to component work.

_{* Current style is subject to change at any time, and are not well documented. To quote a great Australian film, it's just the vibe.}

[ryzngard]

Just some thoughts, but overall like this change. Thanks for cleaning things up :) I didn't check code that was far outside of changed reasons

[alexgav]

[alexgav]

Seems like a good topic for Monday codeabout - just talk through the list of (informal?) conventions we have to make it more explicit (unless there are more pressing topics)

[davidwengier]

Seems like a good topic for Monday codeabout - just talk through the list of (informal?) conventions we have to make it more explicit (unless there are more pressing topics)

LOVE this idea.

[DustinCampbell]

Love it! Many welcome changes here. We can always argue over minor details, but the overall code improvement in this pull request is indisputable.