Update stylelint (#3042)

1. Update `stylelint` dependencies
- As of stylelint v15, we do not need `stylelint-config-prettier`
anymore:
https://github.com/prettier/stylelint-config-prettier/releases/tag/v9.0.5
2. Switch to `stylelint-config-standard`:
`stylelint-prettier/recommended` has not been updated for a long time
and still needs the old `stylelint-config-prettier`
3. Handle new `stylelint` issues

modules/default/newsfeed/newsfeed.css

@@ -1,5 +1,6 @@
 iframe.newsfeed-fullarticle {
   width: 100vw;
+
   /* very large height value to allow scrolling */
   height: 3000px;
   top: 0;