fix experimental feature flag resolution for 'all'

When you have a custom config for the prefix/separator values, then we
want to disable the `oxideParser` for now. But we also have to ensure
that if you use the value `"all"` for the experimental feature flag that
we enable all feature flags.

We were using the keys of the array instead of the values.

Author: RobinMalfait

src/util/normalizeConfig.js

@@ -299,7 +299,7 @@ export function normalizeConfig(config) {
   if (config.prefix !== '' || config.separator !== ':') {
     if (config.experimental === 'all') {
       config.experimental = {}
-      for (let key in featureFlags.experimental) {
+      for (let key of featureFlags.experimental) {
         config.experimental[key] = true
       }
     } else {