sources attribute in sourcemap generated by Vite dev server does not contain directories

[wintenbb]

Describe the bug

When running vite dev server, a sourcemap is attached to generated sources. However, the "sources" attribute contains only the name of the source file (and not the directories).

Reproduction

https://stackblitz.com/edit/vitejs-vite-tjcfaa5t

Steps to reproduce

Look at the sourcemap of src/components/HelloWorld.vue, decode base64

{
  "file": "/home/projects/vitejs-vite-tjcfaa5t/src/components/HelloWorld.vue",
  ...
  "sources": ["HelloWorld.vue"],
  ...
}

### System Info

```shell
System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 20.19.1 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.8.2 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @vitejs/plugin-vue: ^6.0.0 => 6.0.0 
    vite: ^7.0.0 => 7.0.0

Used Package Manager

npm

Logs

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[sapphi-red]

The spec allows a relative path.
https://tc39.es/ecma426/#sec-source-map-format:~:text=The%20sources%20field%20is%20a%20list%20of%20original%20sources%20used%20by%20the%20mappings%20field.%20Each%20entry%20is%20either%20a%20string%20that%20is%20a%20(potentially%20relative)%20URL%20or%20null%20if%20the%20source%20name%20is%20not%20known.