Add upcoming feature flag for SE-409 (#430)

Until the Swift evolution parsing tool is updated, upcoming
feature flags are included in the JavaScript that generates
the Swift evolution dashboard.

This adds the upcoming feature flag for SE-409.

Author: dempseyatgithub

assets/javascripts/swift-evolution.js

@@ -50,6 +50,7 @@ const upcomingFeatureFlags = new Map([
   ['SE-0354', 'BareSlashRegexLiterals'],
   ['SE-0384', 'ImportObjcForwardDeclarations'],
   ['SE-0401', 'DisableOutwardActorInference'],
+  ['SE-0409', 'InternalImportsByDefault'],
 ])
 
 /** Storage for the user's current selection of filters when filtering is toggled off. */