Fix the support for `inject-loader` in v9

[Nikola Pejoski]

inject-loader does not support ES6 modules. To be able to run unit tests that are using this loader we need to have transpiled modules to commonjs.

Also the eslint rule import/no-webpack-loader-syntax should be disabled to allow imports as 'inject-loader!./path/to/module

[Fernando Via Canel]

I believe you @npejo and @pirelenito have some links to a discussion in the Webpack community about how to solve this issue, would you mind pasting it here for context? I would like to know for sure that Webpack is providing support for inject-loader before we move in any direction.