Add getOrInsert() to the Maps group (#3688)

Author: foolip

features/getorinsert.yml

@@ -1,6 +1,7 @@
 name: Map getOrInsert()
 description: The `getOrInsert()` and `getOrInsertComputed()` methods of `Map` objects get a value, setting and getting a default value if needed.
 spec: https://tc39.es/proposal-upsert/
+group: maps
 compat_features:
   - javascript.builtins.Map.getOrInsert
   - javascript.builtins.Map.getOrInsertComputed