Support `layer()` option in `@import`

[forestream]

globalCss({
   imports: [
     'https://cdn.jsdelivr.net/npm/quill@2.0.3/dist/quill.snow.css layer(t)',
   ],
})

I was trying to use layer() css function to override some styles for dark theme, and found out that the above lines are transpiled as below:

@import "https://cdn.jsdelivr.net/npm/quill@2.0.3/dist/quill.snow.css layer(t)";

which doesn't work and has to be:

@import "https://cdn.jsdelivr.net/npm/quill@2.0.3/dist/quill.snow.css" layer(t);

Seems like it needs fixing.
My current workaround is to use <style />