Updated webpack-dev-middleware to v2

[donaldpipowitch]

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• If you are making substantial changes, consider adding a tslint.json containing { "extends": "dtslint/dt.json" }.

cc @shellscape: Does this cover the changes correctly?

[shellscape]

@donaldpipowitch thanks for the ping 😄 I'm no TypeScript expert, but that appears correct. I'll also link to this in the README for folks who need this typedef.

[donaldpipowitch]

Thank you for reviewing this! ♥️

[typescript-bot]

After 5 days, no one has reviewed the PR 😞. A maintainer will be reviewing the PR in the next few days and will either merge it or request revisions. Thank you for your patience!

[Flarna]

This change broke karma-webpack and koa-webpack as they still use webpack-dev-middleware in v1 (see referenced PRs). Maybe v1 typings should be kept?

[shellscape]

koa-webpack will be updated to use wdm@2 soonish. the webpack team is testing leveraging that package and we've got some tests to run yet. If this package is versioned properly, it shouldn't have caused any havok (and I don't mean that to insinuate that it is not)

[paulvanbrenk]

Didn't realize that these changes were in 2.x and the typing was still targeting 1.x, the correct way to handle would've been to have kept a v1 folder for the original typings. @donaldpipowitch can you make that change?

https://github.com/DefinitelyTyped/DefinitelyTyped#i-want-to-update-a-package-to-a-new-major-version

[Flarna]

Regarding tests: There was an issue (#22172) causing that dependents were not tested which is fixed meanwhile.
Not sure if it is worth to keep a V1 version if dependents get updated soon anyway. The two fixes I proposed are simple and should be ok till update is done.

[donaldpipowitch]

Oh snap. This slipped through... This should have been a new major version as announced in the title, but I forgot to update the file header. I'm sorry. Sadly I have no computer for some days. It would be great if this could be fixed by someone until I'm back again.

Sorry.

[donaldpipowitch]

First attempt to fix this PR: #22661.