Codegen: Add JNI C++ generator for TurboModule subclasses

Summary:
This adds the C++ classes for Android, just like checked in here: https://github.com/facebook/react-native/tree/master/ReactAndroid/src/main/java/com/facebook/fbreact/specs/jni

The whitespace/formatting is slightly different but the functionality should be preserved.

Changelog: [Internal]

Reviewed By: mdvacca

Differential Revision: D23489368

fbshipit-source-id: 60c112a48b6de2d2eb19f7d1bcc894048334610f

packages/react-native-codegen/src/generators/modules/GenerateModuleJniH.js

@@ -0,0 +1,78 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict
+ * @format
+ */
+
+'use strict';
+
+import type {SchemaType} from '../../CodegenSchema';
+
+type FilesOutput = Map<string, string>;
+
+const moduleTemplate = `/**
+ * JNI C++ class for module '::_MODULE_NAME_::'
+ */
+class JSI_EXPORT Native::_MODULE_NAME_::SpecJSI : public JavaTurboModule {
+public:
+  Native::_MODULE_NAME_::SpecJSI(const JavaTurboModule::InitParams &params);
+};
+`;
+
+const template = `
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * ${'@'}generated by codegen project: GenerateModuleJniH.js
+ */
+
+#import <ReactCommon/JavaTurboModule.h>
+#import <ReactCommon/TurboModule.h>
+#import <fb/fbjni.h>
+#import <jsi/jsi.h>
+
+namespace facebook {
+namespace react {
+
+::_MODULES_::
+
+} // namespace react
+} // namespace facebook
+`;
+
+module.exports = {
+  generate(
+    libraryName: string,
+    schema: SchemaType,
+    moduleSpecName: string,
+  ): FilesOutput {
+    const nativeModules = Object.keys(schema.modules)
+      .sort()
+      .map(moduleName => {
+        const modules = schema.modules[moduleName].nativeModules;
+        if (modules == null) {
+          return null;
+        }
+
+        return modules;
+      })
+      .filter(Boolean)
+      .reduce((acc, components) => Object.assign(acc, components), {});
+
+    const modules = Object.keys(nativeModules)
+      .map(name => moduleTemplate.replace(/::_MODULE_NAME_::/g, name))
+      .join('\n');
+
+    const fileName = `${moduleSpecName}.h`;
+    const replacedTemplate = template.replace(/::_MODULES_::/g, modules);
+
+    return new Map([[fileName, replacedTemplate]]);
+  },
+};