Fix file-loader compat issue in webpacker 5

[amoshydra]

Change file-loader esModule option to false

Resolve #2613

[aried3r]

@gauravtiwari, what do you think about #2613 (comment)? It seems going forward, many loaders will have esModule: true, or the option added, and the problem here seemed to be that we treated font files etc as ES modules.

https://github.com/webpack-contrib/css-loader/blob/master/CHANGELOG.md#400-2020-07-25
webpack-contrib/mini-css-extract-plugin#475
webpack-contrib/style-loader#441
https://github.com/webpack-contrib/url-loader/blob/master/CHANGELOG.md#300-2019-11-26
https://github.com/webpack-contrib/file-loader/blob/master/CHANGELOG.md#500-2019-11-22

Friendly ping to @jakeNiemiec.

[gauravtiwari]

Yes, I did, thank you.

I think at the moment it's pretty much static files: https://github.com/rails/webpacker/blob/master/lib/install/config/webpacker.yml#L21 so for general usage lets make it default to false.

I believe a lot of people would run this problem but happy to look into a simple configurable solution later.

[renchap]

This is a breaking change and should have been in a major version, or at least documented in the changelog.

If you used for example require("./file.svg").default to get the path of a SVG file, this changes your path to be undefined, and images to be empty if you used it like <img src=…>