feat: support module_version for add-to-app releases

Adds SHOREBIRD_MODULE_VERSION env var support to compileShorebirdYaml.
When set, the value is written into the compiled shorebird.yaml as
module_version, which the updater then sends to the server (alongside
release_version) for add-to-app patch lookup.

The shorebird CLI passes this env var through when running
`flutter build aar` or `flutter build ios-framework` for module
releases (see shorebirdtech/shorebird#3674).

Author: eseidel

packages/flutter_tools/lib/src/shorebird/shorebird_yaml.dart

@@ -72,5 +72,9 @@ Map<String, dynamic> compileShorebirdYaml(
   if (shorebirdPublicKeyEnvVar != null) {
     compiled['patch_public_key'] = shorebirdPublicKeyEnvVar;
   }
+  final String? moduleVersion = environment['SHOREBIRD_MODULE_VERSION'];
+  if (moduleVersion != null) {
+    compiled['module_version'] = moduleVersion;
+  }
   return compiled;
 }

packages/flutter_tools/test/general.shard/shorebird/shorebird_yaml_test.dart

@@ -83,6 +83,29 @@ patch_verification: strict
         'patch_public_key': '4-a',
       });
     });
+    test('module_version from environment', () {
+      const String yamlContents = '''
+app_id: 1-a
+''';
+      final YamlDocument input = loadYamlDocument(yamlContents);
+      final YamlMap yamlMap = input.contents as YamlMap;
+
+      // Without env var, module_version is absent.
+      final Map<String, dynamic> withoutEnv = compileShorebirdYaml(
+        yamlMap,
+        flavor: null,
+        environment: <String, String>{},
+      );
+      expect(withoutEnv.containsKey('module_version'), isFalse);
+
+      // With env var, module_version is included.
+      final Map<String, dynamic> withEnv = compileShorebirdYaml(
+        yamlMap,
+        flavor: null,
+        environment: <String, String>{'SHOREBIRD_MODULE_VERSION': 'abc1234'},
+      );
+      expect(withEnv['module_version'], 'abc1234');
+    });
     test('edit in place', () {
       const String yamlContents = '''
 app_id: 1-a