[plugin-webpack] Webpack plugin should use eval source maps in development to significantly speed up builds

[lostfictions]

Preflight Checklist

• I have read the contribution documentation for this project.
• I agree to follow the code of conduct that this project follows, as appropriate.
• I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Problem Description

Hey there, if I'm not mistaken it seems @electron-forge/plugin-webpack has a suboptimal devtools configuration for development:

https://github.com/electron-userland/electron-forge/blob/90f122c2f6000a1cd10f71dd8d4edc9e483c99cd/packages/plugin/webpack/src/WebpackConfig.ts#L144

https://github.com/electron-userland/electron-forge/blob/90f122c2f6000a1cd10f71dd8d4edc9e483c99cd/packages/plugin/webpack/src/WebpackConfig.ts#L216

In my experience (and per webpack documentation), something like eval-cheap-module-source-map might be significantly faster in development. (I'm also not certain why inline-source-map would be used for the renderer process, even in production.)

Proposed Solution

Switch between eval-cheap-module-source-map (or eval-source-map if slower builds but column-accurate source maps are preferable) and source-map depending on whether webpack is bundling for development or for production.

Happy to submit a PR for this, but just wanted to check in that there's no caveat to Electron that I'm missing that justifies the current approach!

[malept]

This was done in #2225