chore: fix missing style sources

[NicoPennec]

Describe your changes

Embed sources in the source map to fix a warning when using vue-datepicker with Vite.

$ vite

> Sourcemap for "/../my-vue-project/node_modules/@vuepic/vue-datepicker/dist/main.css" points to missing source files

Issue ticket number and link

Fixes #1226

Checklist before requesting a review

• I have performed a self-review of my code
• I have ensured that unit tests pass without errors
• If it is a new feature, I have added a new unit test