Tool refactoring to reduce code duplication

[TrueDoctor]

Restructure how the tool handles internal states such as currently pressed modifier keys. And we might need a way to share code between tools to reduce the amount of code duplication.

See also the related issue #151.

Complexity: 2
Involves: Editor (Rust)

[Keavon]

@pkupper I believe this is a continuation of work you began when you did your first tool-related tasks. Is that correct? If this task wasn't your idea, I may be attributing my memory to the wrong person, sorry if that's the case.

This is soft-blocking work on additional tools, I believe (but correct me if I'm wrong). Could you update on the status of what this task entails and how important it is for working on new tools like the Pen Tool, Path Tool, and Text Tool? I know you are busy with #140 and #145 presently, but would you also be able to tackle and complete this over the weekend so work can begin on the crucial Path Tool (#82) and Pen Tool (#185)?

[Keavon]

Some loose notes on this subject from @TrueDoctor:

I would suggest unifying the approach for keeping internal states by having one "macro state" and modifiers e.g.

(Ready, Modifiers{center, keep_aspect_ratio})

with something like:

(state, mod, Message::LockAspectRatio) => {mod.aspect_ratio = true; state}

that should reduce some of the code duplication

we will probably still need a better approach for the make_operation function