build in modern mode

[beeplin]

The original vue cli 3 supports amazing modern mode which is not currently supported by yarn ssr:build.

[phil294]

I just tried to implement this in #199. You can use it, but modern mode is currently not configurable but baked in, and it's not thoroughly tested.
Since it all stronlgy relies on the internal workings of vue cli (ModernModePlugin), all this is not very pretty and it feels like the best solution would be to wait for (or participate in) a rewrite of vue's template renderer and/or modern mode :/

[chemparparokke]

@Akryum @vue/cli got an update up to next version. Any chance to get support of modern build in vue-cli-plugin-ssr? 🙏