Expose C++ TurboModule codegen

Summary:
This adjusts the previously unused (but fully working!) `rn_codegen_cxx_modules` rule to be consistent with the other codegen rules and calls it from the `rn_codegen` with the "JSI" suffix to not conflict with the other rules, and to match the convention established by hand-written C++ TurboModules.

Changelog:
Internal

Reviewed By: RSNara

Differential Revision: D34451208

fbshipit-source-id: 4d779b068dfa4f7fd73fd3bca354fffe86d01f73

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

@@ -85,7 +85,7 @@ const FileTemplate = ({
  * ${'@'}generated by codegen project: GenerateModuleH.js
  */
 
-#include <react/modules/${libraryName}/NativeModules.h>
+#include "${libraryName}JSI.h"
 
 namespace facebook {
 namespace react {
@@ -221,7 +221,7 @@ module.exports = {
       })
       .join('\n');
 
-    const fileName = 'NativeModules.cpp';
+    const fileName = `${libraryName}JSI-generated.cpp`;
     const replacedTemplate = FileTemplate({
       modules,
       libraryName,