web file transfer (#9587)

Signed-off-by: 21pages <sunboeasy@gmail.com>

flutter/lib/web/dummy.dart

@@ -0,0 +1,14 @@
+Future<void> webselectFiles({required bool is_folder}) async {
+  throw UnimplementedError("webselectFiles");
+}
+
+Future<void> webSendLocalFiles(
+    {required int handleIndex,
+    required int actId,
+    required String path,
+    required String to,
+    required int fileNum,
+    required bool includeHidden,
+    required bool isRemote}) {
+  throw UnimplementedError("webSendLocalFiles");
+}