SSR cannot generate assets preloading scripts (assets in resources hints)

[clarkdo]

Hi team 😸, thank you so much for providing the excellent project and support.

Currently we are working on the upgrading to Webpack4 in Nuxt, we met an issue in font preloading of SSR, the preload scripts of assets are empty (ssrContext.renderResourceHints()).

After some investigations, I found the font asset issue was caused by two reasons.

1. Webpack module assets is null, I have opened a pr fix: module assets is in buildInfo webpack/webpack#6640 (merged)
2. Webpack ConcatenatedModule has changed module identifier to request + additional hash, but vue-loader is still using request
ConcatenatedModule: https://github.com/webpack/webpack/blob/master/lib/optimize/ConcatenatedModule.js#L434
   SSR plugin is using identifier which is modified by ConcatenatedModule: https://github.com/vuejs/vue/blob/dev/src/server/webpack-plugin/client.js#L46
   vue-loader is using request: https://github.com/vuejs/vue-loader/blob/master/lib/loader.js#L250

I'm not very sure the fix should be done in vue-ssr or vue-loader, so just opened issue here, we can have a discussion and figure out the solution 😸