fix(types): Switch compilation type in error handler to unknown

[lobsterkatie]

Two years ago, we modified the errorHandler option to take a third argument, of the type Compilation. Though the contents of the type exists in similar forms in webpack 4 and 5, in webpack 4 it's exported as compilation.Compilation, where as in webpack 5, it's exported at the top-level.

This didn't matter much until about a month ago, when #308 updated the overall options type to reflect the addition of the third argument for errorHandler. That change was released three days ago, in v 1.17.2. Because that PR used Compilation in its webpack 5/top-level form, anyone using this plugin together with webpack 4 and TS will receive the following error when they import the plugin (assuming they have skipLibCheck set to false in their TS config):

This fixes that by using unknown as the type instead, and updates the docstring with a note about the above. It also changes the dev dependencies for webpack and @types/webpack. Even though the new version requirements will always result in 5.x getting installed, keeping the 4.41.31 entry is a reminder to anyone reading the file that a) we should preserve compatibility with 4.x, and b) that that's the minimum 4.x version we need to worry about (see here).

Fixes #321.

[rchl]

Do we actually need 4.41.31 to be set as a minimum version?
Nuxt 3 uses 4.41.30 (the latest released version even older 4.41.28) currently so that would result in two different versions and potentially issues.
https://github.com/nuxt/nuxt.js/blob/034b9901df8a304c6a97cf649a07cba7fbc55446/packages/types/package.json#L28

[kamilogorek]

Yes, please see: #296 (comment)

[rchl]

That one only mentions 4.41.23 as a required minimum but this PR sets the minimum to 4.41.31.

[kamilogorek]

Oh, I think we could stick with 4.41.23 then, but I see that webpack team is scraping old versions or something, as I cannot event find then anymore:
https://www.npmjs.com/package/webpack/v/4.41.23
https://www.npmjs.com/package/webpack/v/4.41.31

cc @lobsterkatie

[rchl]

It's the @types/webpack we are talking about - https://www.npmjs.com/package/@types/webpack/v/4.41.23

EDIT: Well, I guess we are talking about both but probably those don't have to be entirely in sync.
As far as Nuxt, it uses webpack ^4.46.0:
https://github.com/nuxt/nuxt.js/blob/034b9901df8a304c6a97cf649a07cba7fbc55446/packages/webpack/package.json#L51-L51