Turbopack supports importing inline CSS via `data:text/css,...` and
`data:text/css+module,...` data URLs. Vite/Rolldown treats `data:`
specifiers as external, so the literal URL was reaching the bundled
output and Node/workerd refused to load it with
`ERR_UNKNOWN_MODULE_FORMAT: Unknown module format: text/css+module`,
breaking the entire build for any app that adopted the Turbopack-only
syntax (e.g. test/e2e/app-dir/css-modules-data-urls).
Add a pre-transform that rewrites these imports into synthetic
`\0vinext-data-css/<hash>.module.css` (or `.css`) specifiers. Vite's
existing CSS pipeline (LightningCSS, CSS modules) then handles
class-name hashing, JS export map generation, and stylesheet asset
emission. The decoded payload is cached by synthetic id so the same
data URL imported from RSC and client environments deduplicates the
way real CSS imports do.
Closes#1363
James Anderson