Chunk names are not respected under --target lib

[doublemarked]

Version

3.0.0-beta.9

Reproduction link

https://github.com/doublemarked/vue-libconf-issues

Steps to reproduce

1. git clone https://github.com/doublemarked/vue-libconf-issues.git
2. npm install && npm run build
3. Observe filenames in dist/ are using chunk ids, not names, despite webpackChunkName settings during import in index.js

What is expected?

Application of webpackChunkName: "name" during import should influence output filenames.

What is actually happening?

Chunks are grouped based on webpackChunkName but filenames use chunk ids (numbers).

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Recent PR #1173 made it possible to specify chunk names for app builds, but this configuration is clobbered by the lib build configuration. These settings should also be applied when building with --target lib.