src: add Env() to AsyncContext

PR-URL: nodejs/node-addon-api#568
Reviewed-By: NickNaso <nicoladelgobbo@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

doc/async_context.md

@@ -45,6 +45,16 @@ The `Napi::AsyncContext` to be destroyed.
 virtual Napi::AsyncContext::~AsyncContext();
 ```
 
+### Env
+
+Requests the environment in which the async context has been initially created.
+
+```cpp
+Napi::Env Env() const;
+```
+
+Returns the `Napi::Env` environment in which the async context has been created.
+
 ## Operator
 
 ```cpp

napi-inl.h

@@ -3589,6 +3589,10 @@ inline AsyncContext::operator napi_async_context() const {
   return _context;
 }
 
+inline Napi::Env AsyncContext::Env() const {
+  return Napi::Env(_env);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // AsyncWorker class
 ////////////////////////////////////////////////////////////////////////////////

napi.h

@@ -1784,6 +1784,8 @@ namespace Napi {
 
     operator napi_async_context() const;
 
+    Napi::Env Env() const;
+
   private:
     napi_env _env;
     napi_async_context _context;