Refactor core type generics naming

[baileytincher]

Somewhat a WIP still. It would be good to come up with a way to test type definitions more thoroughly though. One option is to move some (or all) of the test files to TypeScript and that will naturally catch some potential breaking changes in future PRs.

I found the use of the EventType and HandlerReturnType definitions to be confusing as I was working on this. I think they can be simplified or removed entirely, but I'm going to mull over their purpose a bit. Would appreciate input on what they are meant to do as I did not find a need for such a construct in working on my own framework https://github.com/ShallotJS/shallot/blob/4781b6700e637d1e15dedf99d5202ddd799888b8/src/aws/index.ts#L44-L52

What does this implement/fix? Explain your changes.

• Renames unclear generics in the type definitions of middy core.
• Renames ambiguous references/imports.
• Replaces all uses of any with unknown https://stackoverflow.com/questions/51439843/unknown-vs-any

Does this close any currently open issues?

#585 (comment)

Todo list

[ ] Feature/Fix fully implemented
[ ] Added tests
[ ] Updated relevant documentation
[ ] Updated relevant examples

[lmammino]

Great contribution @baileytincher! Thanks a lot.

How would you suggest to test these changes?

Also, be aware that the CI is currently failing the linting step.

[willfarrell]

I think the linting error was from some earlier incomplete code I pushed. It was fixed last night. Re-pull, to resolve it.

[willfarrell]

Closing in favour of #616