initial pwa + custom tabs

packages/flutter_mozilla_components/lib/flutter_mozilla_components.dart

@@ -58,6 +58,7 @@ export 'src/pigeons/gecko.g.dart'
         GeckoFetchResponse,
         GeckoPref,
         GeckoPublicSuffixListApi,
+        GeckoPwaApi,
         GeckoSitePermissionsApi,
         GeckoSuggestion,
         GeckoSuggestionType,
@@ -75,6 +76,8 @@ export 'src/pigeons/gecko.g.dart'
         MlProgressStatus,
         MlProgressType,
         PhoneHitResult,
+        PwaIcon,
+        PwaManifest,
         QueryParameterStripping,
         Resource,
         ResourceSize,

packages/flutter_mozilla_components/lib/src/domain/services/gecko_event.dart

@@ -202,8 +202,12 @@ class GeckoEventService extends GeckoStateEvents {
     _mlProgressSubject.addWhenMoreRecent(sequence, null, progress);
   }
 
-  void onMlProgress(int timestamp, MlProgressData progress) {
-    _mlProgressSubject.addWhenMoreRecent(timestamp, null, progress);
+  @override
+  void onManifestUpdate(int sequence, String tabId, PwaManifest? manifest) {
+    _manifestUpdateSubject.addWhenMoreRecent(sequence, tabId, (
+      tabId: tabId,
+      manifest: manifest,
+    ));
   }
 
   GeckoEventService.setUp({