feat: split triggers in matcher.rs into categories with explanations

[hippietrail]

I know the logic here is up for replacement but I think this categorization will still help in various ways:

1. It will help elucidate different classes and types of replacements.

2. It will help us see which categories will be amenable to various kinds of automation.

3. It will help curators adding more lints in the meantime.

4. It also shows that some lints combine multiple kinds of problems while others don't fit well into any neat category. There is some fuzziness.

(I first sorted them alphabetically then grouped them, so the groups themselves are more in a kind of alphabetical order than any semantic order.)

[elijah-potter]

This PR isn't super helpful. I appreciate the thought, but it feels like busy work.

Your changes also significantly increase the construction cost of the Matcher by allocating more than the previous implementation. It's an acceptable cost under most circumstances, but it underlines why reviewing this kind of change is non-trivial.

I'll merge it, but next time include it in another PR so I can review it as a whole, rather than as a part.

That said, you've been incredibly helpful to the development of Harper. I appreciate it immensely. Keep up the good work!

[hippietrail]

This PR isn't super helpful. I appreciate the thought, but it feels like busy work.

It was partly because in testing things kept leading me here so I wanted to understand it to see what kind of replacements are done where and add more of the same. For instance it wasn't clear to me before this that what could be considered diverse jobs were all done in one place.

Your changes also significantly increase the construction cost of the Matcher by allocating more than the previous implementation. It's an acceptable cost under most circumstances, but it underlines why reviewing this kind of change is non-trivial.

Ah I wasn't sure about that. I could also do it in one function call with just comments interspersed to describe the sections.

I'll merge it, but next time include it in another PR so I can review it as a whole, rather than as a part.

I'm not sure what you about in another PR or what it's part of now. Sorry.

That said, you've been incredibly helpful to the development of Harper. I appreciate it immensely. Keep up the good work!

Thank you! So far it keeps inspiring me with more ideas, and something real to properly learn Rust.