JIT: Add support for before/after pseudo-elements (#4461)

src/plugins/content.js

@@ -0,0 +1,5 @@
+import createUtilityPlugin from '../util/createUtilityPlugin'
+
+export default function () {
+  return createUtilityPlugin('content')
+}

src/plugins/index.js

@@ -161,3 +161,5 @@ export { default as transitionProperty } from './transitionProperty'
 export { default as transitionDelay } from './transitionDelay'
 export { default as transitionDuration } from './transitionDuration'
 export { default as transitionTimingFunction } from './transitionTimingFunction'
+
+export { default as content } from './content'