[macros] Add standalone program for the example observable macro (#3578)

* add standalone observable example

* update to latest SDK

* update analyzer excludes

working/macros/example/analysis_options.yaml

@@ -9,3 +9,4 @@ analyzer:
     - bin/injectable_main.dart
     - bin/user_main.dart
     - bin/json_serializable_main.dart
+    - bin/observable_main.dart

working/macros/example/bin/observable_main.dart

@@ -0,0 +1,21 @@
+import 'package:macro_proposal/observable.dart';
+
+void main() {
+  var jack = ObservableUser(age: 10, name: 'jack');
+  jack.age = 12;
+  jack.name = 'john';
+}
+
+class ObservableUser {
+  @Observable()
+  int _age;
+
+  @Observable()
+  String _name;
+
+  ObservableUser({
+    required int age,
+    required String name,
+  }) : _age = age,
+       _name = name;
+}

working/macros/example/pubspec.yaml

@@ -17,84 +17,84 @@ dependency_overrides:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/_fe_analyzer_shared
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   _js_interop_checks:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/_js_interop_checks
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   analyzer:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/analyzer
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   build_integration:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/build_integration
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   compiler:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/compiler
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   dart2js_info:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/dart2js_info
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   dart2wasm:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/dart2wasm
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   dev_compiler:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/dev_compiler
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   front_end:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/front_end
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   frontend_server:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/frontend_server
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   js_ast:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/js_ast
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   js_runtime:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/js_runtime
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   js_shared:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/js_shared
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   kernel:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/kernel
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   mmap:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/mmap
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   vm:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/vm
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev
   wasm_builder:
     git:
       url: https://github.com/dart-lang/sdk.git
       path: pkg/wasm_builder
-      ref: 3.3.0-238.0.dev
+      ref: 3.4.0-56.0.dev