Add support for /? to alias to --help (flutter#172328)

Closes flutter#70616.

Author: matanlurey

packages/flutter_tools/lib/executable.dart

@@ -65,11 +65,15 @@ Future<void> main(List<String> args) async {
   final bool veryVerbose = args.contains('-vv');
   final bool verbose = args.contains('-v') || args.contains('--verbose') || veryVerbose;
   final bool prefixedErrors = args.contains('--prefixed-errors');
-  // Support the -? Powershell help idiom.
+  // Support universal help idioms.
   final int powershellHelpIndex = args.indexOf('-?');
   if (powershellHelpIndex != -1) {
     args[powershellHelpIndex] = '-h';
   }
+  final int slashQuestionHelpIndex = args.indexOf('/?');
+  if (slashQuestionHelpIndex != -1) {
+    args[slashQuestionHelpIndex] = '-h';
+  }
 
   final bool doctor =
       (args.isNotEmpty && args.first == 'doctor') ||

packages/flutter_tools/test/integration.shard/command_output_test.dart

@@ -42,6 +42,19 @@ void main() {
     );
   });
 
+  testWithoutContext('Flutter help is shown with /? command line argument', () async {
+    final ProcessResult result = await processManager.run(<String>[flutterBin, '/?']);
+
+    // Development tools.
+    expect(
+      result.stdout,
+      contains(
+        'Run "flutter help <command>" for more information about a command.\n'
+        'Run "flutter help -v" for verbose help output, including less commonly used options.',
+      ),
+    );
+  });
+
   testWithoutContext('flutter doctor is not verbose', () async {
     final ProcessResult result = await processManager.run(<String>[flutterBin, 'doctor', '-v']);