Add native delta client for Metro

Summary:
Adds C++ delta client that keeps modules in memory, and can be used as a RAM bundle.

For now, this client expects a `folly::dynamic` object as payload for patches, i.e. the JSON response retrieved from Metro needs to be parsed with `folly::parseJson` by the caller.

In the future, we will replace JSON with a streaming friendly binary format.

Reviewed By: fromcelticpark

Differential Revision: D7845136

fbshipit-source-id: f003f98a2607c8354c427a7e60e01e19e20295b1

ReactAndroid/src/main/jni/react/jni/JniJSModulesUnbundle.cpp

@@ -82,7 +82,7 @@ JSModulesUnbundle::Module JniJSModulesUnbundle::getModule(uint32_t moduleId) con
     buffer = static_cast<const char *>(AAsset_getBuffer(asset.get()));
   }
   if (buffer == nullptr) {
-    throw ModuleNotFound("Module not found: " + sourceUrl);
+    throw ModuleNotFound(moduleId);
   }
   return {sourceUrl, std::string(buffer, AAsset_getLength(asset.get()))};
 }