External source map support (colocated .js.map files)

Do you want to request a feature or report a bug? Feature

What is the current behavior? Inline source maps work, but .js.map files are not used

What is the expected behavior? Colocated .js.map source maps work as well as inline maps

https://github.com/facebook/jest/issues/336#issuecomment-376228890 indicated a PR for this is welcome. I can look into this if I have time and I can get the CLA cleared from employer but wanted a place to track progress either way :)

perhaps just need to hook into the lines below? GitHub search isn't the best... https://github.com/facebook/jest/blob/23eec748db0de7b6b5fcda28cc51c48ddae16545/packages/jest-runtime/src/index.js#L541-L546