Bug 1945252 - Part 1: Use the GeckoView ExternalHelperAppService on iOS, r=glandium

This is the backend used on Android, and we plan to use the same architecture
on iOS.

Differential Revision: https://phabricator.services.mozilla.com/D236401

docshell/build/components.conf

@@ -164,7 +164,7 @@ if defined('MOZ_ENABLE_DBUS'):
         },
     ]
 
-if buildconfig.substs['MOZ_WIDGET_TOOLKIT'] == 'android':
+if buildconfig.substs['MOZ_WIDGET_TOOLKIT'] in ('android', 'uikit'):
     Classes += [
         # Android has its own externel-helper-app-service, so we omit
         # that here for nsExternalHelperAppService.

uriloader/exthandler/uikit/nsOSHelperAppService.mm

@@ -53,6 +53,7 @@ NS_IMETHODIMP
 nsOSHelperAppService::GetProtocolHandlerInfoFromOS(const nsACString& aScheme,
                                                    bool* found,
                                                    nsIHandlerInfo** _retval) {
-  *found = false;
-  return NS_OK;
+  // We don't want to get protocol handlers from the OS in GV; the app
+  // should take care of that in NavigationDelegate.onLoadRequest().
+  return NS_ERROR_NOT_IMPLEMENTED;
 }