Describe the bug

PR #6251 introduced a separate chunk for async imports to improve cache hits which is great to have.

The problem is it generates a single chunk for all async imports, which results in all packages imported async-ly to be packed into one huge(in my case >1MB) file.

I think it should be at least keyed chunks so packages from different async chunks will be written separately.

vite v2.7.7:

vite v2.7.8:

Reproduction

https://github.com/QiroNT/vite-reps/tree/vite-6251

System Info

System:
    OS: Linux 5.14 Manjaro Linux
    CPU: (12) x64 AMD Ryzen 5 3600 6-Core Processor
    Memory: 12.65 GB / 31.30 GB
    Container: Yes
    Shell: 5.1.12 - /bin/bash
  Binaries:
    Node: 17.3.0 - ~/.local/share/pnpm/node
    npm: 8.3.0 - ~/.local/share/pnpm/npm
  Browsers:
    Firefox: 95.0.1
  npmPackages:
    @vitejs/plugin-vue: ^2.0.1 => 2.0.1 
    vite: ^2.7.8 => 2.7.8

Used Package Manager

pnpm

Logs

No response

Validations

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• The provided reproduction is a minimal reproducible example of the bug.