[iOS][WidgetKit] Enable extension by default in ToT

Bug: 1138702

Change-Id: Ic2ba09f4e6eab748f93ca9aee4fc2cbd0bf70532
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2517993
Commit-Queue: Javier Flores <javierrobles@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825491}

ios/build/chrome_build.gni

@@ -12,7 +12,7 @@ declare_args() {
   ios_enable_search_widget_extension = true
 
   # Enable iOS 14, WidgetKit extension.
-  ios_enable_widget_kit_extension = false
+  ios_enable_widget_kit_extension = true
 
   # Enable iOS 14, WidgetKit extension (prebuilt).
   ios_enable_prebuilt_widget_kit_extension = false