[fuchsia] Fix BUILD and metadata file for Fuchsia (#24294)

examples/flutter_gallery/BUILD.gn

@@ -2,18 +2,42 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("$flutter_root/build/flutter_app.gni")
-
 assert(is_fuchsia)
 
+import("//topaz/runtime/flutter_runner/flutter_app.gni")
+
 flutter_app("flutter_gallery") {
+  package_name = "flutter_gallery"
   main_dart = "lib/main.dart"
 
+  manifest = "pubspec.yaml"
+
   disable_analysis = true
 
+  meta = [
+    {
+      path = rebase_path("meta/flutter_gallery.cmx")
+      dest = "flutter_gallery.cmx"
+    },
+  ]
+
   deps = [
     "../../packages/flutter",
+    "//third_party/dart-pkg/pub/charcode",
+    "//third_party/dart-pkg/pub/collection",
+    "//third_party/dart-pkg/pub/connectivity",
+    "//third_party/dart-pkg/pub/cupertino_icons",
+    "//third_party/dart-pkg/pub/device_info",
+    "//third_party/dart-pkg/pub/flutter_gallery_assets",
+    "//third_party/dart-pkg/pub/meta",
+    "//third_party/dart-pkg/pub/path",
+    "//third_party/dart-pkg/pub/source_span",
+    "//third_party/dart-pkg/pub/string_scanner",
+    "//third_party/dart-pkg/pub/typed_data",
     "//third_party/dart-pkg/pub/url_launcher",
+    "//third_party/dart-pkg/pub/vector_math",
+    "//third_party/dart-pkg/pub/video_player",
+    "//third_party/dart/third_party/pkg/intl",
   ]
 
 }

examples/flutter_gallery/meta/flutter_gallery.cmx

+{
+    "program": {
+        "data": "data/flutter_gallery"
+    },
+    "sandbox": {
+        "system": [ "data" ],
+        "features": [ "persistent-storage" ],
+        "services": [
+            "fuchsia.cobalt.LoggerFactory",
+            "fuchsia.fonts.Provider",
+            "fuchsia.logger.LogSink",
+            "fuchsia.modular.Clipboard",
+            "fuchsia.modular.ContextWriter",
+            "fuchsia.modular.DeviceMap",
+            "fuchsia.modular.ModuleContext",
+            "fuchsia.sys.Environment",
+            "fuchsia.sys.Launcher",
+            "fuchsia.testing.runner.TestRunner",
+            "fuchsia.ui.input.ImeService",
+            "fuchsia.ui.policy.Presenter",
+            "fuchsia.ui.scenic.Scenic",
+            "fuchsia.ui.viewsv1.ViewManager"
+        ]
+    }
+}