fix: directly used mkdirp instead of through Webpack

[JoshuaKGoldberg]

Fixes Webpack 5 usage by no longer requiring the removed webpack/lib/node/NodeOutputFileSystem

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

Fixes #435.

Breaking Changes

Introduces dependency on mkdirp, which was only transient through webpack before.

[alexander-akait]

/cc @hiroppy

[hiroppy]

Thanks.

[zackify]

When will a new release be cut?

[jpreynat]

Could we please have a release to benefit from this update and use it again with latest versions of webpack 5?

[alexander-akait]

In TODO, release will be tomorrow

[jpreynat]

Great, thanks @evilebottnawi

[natew]

Any word on releasing this?

[alexander-akait]

@natew yes, today, we find some problems with api and redesigning it in the next version, so it took us a little longer