No theme.d.ts file in the installed library

[roamiiing]

Describe the bug

I want to use TS for my theme config, but I get the following error:

TS2307: Cannot find module 'vitepress/theme' or its corresponding type declarations.

I think it happens because there is no theme.d.ts in the files array of package.json.

Reproduction

1. Install vitepress
2. Create docs/.vitepress/theme/index.ts file
3. Type import DefaultTheme from 'vitepress/theme'
4. Get the error from the IDE

Expected behavior

No type error

System Info

System:
    OS: macOS 11.3.1
    CPU: (8) x64 Intel(R) Core(TM) i5-8257U CPU @ 1.40GHz
    Memory: 25.62 MB / 8.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 16.4.1 - ~/.nvm/versions/node/v16.4.1/bin/node
    npm: 7.18.1 - ~/.nvm/versions/node/v16.4.1/bin/npm
  Browsers:
    Chrome: 95.0.4638.69
    Firefox Developer Edition: 92.0
    Safari: 14.1
  npmPackages:
    vitepress: ^0.20.1 => 0.20.1

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.

[yyx990803]

#489 (comment)