What:

Fix issue #4354 unknown at-rule expressions should not have commas in keyword list.

Why:

Current behavior (4.4.0+):

.box {
  @apply h-64, w-64;
}

Expected behavior:

.box {
  @apply h-64 w-64;
}

There have been downstream issues, see: web-infra-dev/rsbuild#5688

Checklist:

• Documentation
• Added/updated unit tests
• Code complete

Should be a less hacky solution than #4366
Seems some logic was not needed as tests passed without some problematic code.
I added some additional layer at-rule tests since the regression was caused by code ntroduced to support layer at-rules.