support loaders implemented in ESM

[jablko]

Passing type: "module" to loader-runner will load all loaders with import() vs. require(): https://github.com/webpack/loader-runner/blob/6221befd031563e130f59d171e732950ee4402c6/lib/loadLoader.js#L5-L9

import() supports both ESM and CJS whereas require() was CJS only.

Fixes #13233

[webpack-bot]

For maintainers only:

• This needs to be documented (issue in webpack/webpack.js.org will be filed when merged)
• This needs to be backported to webpack 4 (issue will be created when merged)

[webpack-bot]

@jablko The most important CI builds failed. This way your PR can't be merged.

Please take a look at the CI results from azure (1 errors / 2 warnings) and appveyor (failure) and fix these issues.

[vankop]

duplicate of #15198