Twenty Nineteen: Update PostCSS to version 8.x.

This updates the build processes within Twenty Nineteen to use the latest major version of PostCSS, 8.x.

There are no changes to any built files as a result of these updates.

Props desrosj, peterwilsoncc.
Fixes #57554.

git-svn-id: https://develop.svn.wordpress.org/trunk@55458 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-content/themes/twentynineteen/package.json

@@ -12,8 +12,9 @@
     "chokidar-cli": "^3.0.0",
     "node-sass": "^8.0.0",
     "npm-run-all": "^4.1.5",
-    "postcss-cli": "^7.1.2",
-    "postcss-focus-within": "^4.0.0",
+    "postcss": "^8.4.21",
+    "postcss-cli": "^10.1.0",
+    "postcss-focus-within": "^7.0.2",
     "rtlcss": "^4.0.0"
   },
   "rtlcssConfig": {
@@ -23,7 +24,8 @@
       "clean": true,
       "greedy": false,
       "processUrls": false,
-      "stringMap": []
+      "stringMap": [],
+      "disablePolyfillReadyClass": true
     },
     "plugins": [],
     "map": false

src/wp-content/themes/twentynineteen/postcss.config.js

@@ -8,6 +8,8 @@ module.exports = {
 
 module.exports = {
     plugins: [
-        postcssFocusWithin(/* pluginOptions */)
+        postcssFocusWithin({
+            disablePolyfillReadyClass: true
+        })
     ]
 };