Move annotate from Liquid to info string (#37651)

Co-authored-by: Peter Bengtsson <peterbe@github.com>

lib/render-content/plugins/parse-info-string.js

@@ -0,0 +1,27 @@
+// Based on https://spec.commonmark.org/0.30/#info-string
+// Parse out info strings on fenced code blocks, example:
+// ```javascript lineNumbers:left copy:all annotate
+// becomes...
+// node.lang = javascript
+// node.meta = { lineNumbers: 'left', copy: 'all', annotate: true }
+
+import { visit } from 'unist-util-visit'
+
+const matcher = (node) => node.type === 'code' && node.lang && node.meta
+
+export default function parseInfoString() {
+  return (tree) => {
+    visit(tree, matcher, (node) => {
+      node.meta = strToObj(node.meta)
+    })
+  }
+}
+
+function strToObj(str) {
+  return Object.fromEntries(
+    str
+      .split(/\s+/g)
+      .map((k) => k.split(':'))
+      .map(([k, ...v]) => [k, v.length ? v.join(':') : true])
+  )
+}