Add missing trailing commas (#28673)

* add trailing commas on list/map/parameters

* add trailing commas on Invocation with nb of arg>1

* add commas for widget containing widgets

* add trailing commas if instantiation contains trailing comma

* revert bad change
diff --git a/packages/flutter_tools/lib/src/devfs.dart b/packages/flutter_tools/lib/src/devfs.dart
index 66b473a..05e9292 100644
--- a/packages/flutter_tools/lib/src/devfs.dart
+++ b/packages/flutter_tools/lib/src/devfs.dart
@@ -254,7 +254,7 @@
         params: <String, dynamic> {
           'fsName': fsName,
           'uri': deviceUri.toString(),
-          'fileContents': fileContents
+          'fileContents': fileContents,
         },
       );
     } catch (error) {
@@ -384,7 +384,7 @@
     VMService serviceProtocol,
     this.fsName,
     this.rootDirectory, {
-    String packagesFilePath
+    String packagesFilePath,
   }) : _operations = ServiceProtocolDevFSOperations(serviceProtocol),
        _httpWriter = _DevFSHttpWriter(fsName, serviceProtocol) {
     _packagesFilePath =