Add * variant for targeting direct children (#12551)

* add `*` as child variant

* add `*` as allowed variant character

* update test to reflect Lightning CSS output

* add `childVariant` test

* Update changelog

---------

Co-authored-by: Adam Wathan <4323180+adamwathan@users.noreply.github.com>
Co-authored-by: Robin Malfait <malfait.robin@gmail.com>
Co-authored-by: Gregor Kaczmarczyk <github@aggreggator.de>

src/corePlugins.js

@@ -25,6 +25,9 @@ import { normalize } from './util/dataTypes'
 import { INTERNAL_FEATURES } from './lib/setupContextUtils'
 
 export let variantPlugins = {
+  childVariant: ({ addVariant }) => {
+    addVariant('*', '& > *')
+  },
   pseudoElementVariants: ({ addVariant }) => {
     addVariant('first-letter', '&::first-letter')
     addVariant('first-line', '&::first-line')

src/lib/setupContextUtils.js

@@ -756,6 +756,7 @@ function resolvePlugins(context, root) {
   // TODO: This is a workaround for backwards compatibility, since custom variants
   // were historically sorted before screen/stackable variants.
   let beforeVariants = [
+    variantPlugins['childVariant'],
     variantPlugins['pseudoElementVariants'],
     variantPlugins['pseudoClassVariants'],
     variantPlugins['hasVariants'],