Add js engine information in React Native error reporting

Summary:
To avoid "js engine: ..." appearing everywhere, only add this information
to the error message when react native is reporting errors to the server.

Reviewed By: yungsters

Differential Revision: D9754371

fbshipit-source-id: a8001480c75ccf93c953c79f26470df678871cb3

Libraries/Core/Devtools/parseErrorStack.js

@@ -19,6 +19,7 @@ export type StackFrame = {
 
 export type ExtendedError = Error & {
   framesToPop?: number,
+  jsEngine?: string,
 };
 
 function parseErrorStack(e: ExtendedError): Array<StackFrame> {