src: move v8::HandleScope call to Emit

Move v8::HandleScope call to Emit removing it from previous locations
where it was added to avoid crashing (constructor and destructor of
AsyncWrap) for a more general and fool-proof solution.

Ref: nodejs#19972 (comment)

src/async_wrap-inl.h

@@ -50,15 +50,13 @@ inline AsyncWrap::AsyncScope::AsyncScope(AsyncWrap* wrap)
   Environment* env = wrap->env();
   if (env->async_hooks()->fields()[Environment::AsyncHooks::kBefore] == 0)
     return;
-  v8::HandleScope handle_scope(env->isolate());
   EmitBefore(env, wrap->get_async_id());
 }
 
 inline AsyncWrap::AsyncScope::~AsyncScope() {
   Environment* env = wrap_->env();
   if (env->async_hooks()->fields()[Environment::AsyncHooks::kAfter] == 0)
     return;
-  v8::HandleScope handle_scope(env->isolate());
   EmitAfter(env, wrap_->get_async_id());
 }
 

src/async_wrap.cc

@@ -169,6 +169,7 @@ void Emit(Environment* env, double async_id, AsyncHooks::Fields type,
   if (async_hooks->fields()[type] == 0)
     return;
 
+  v8::HandleScope handle_scope(env->isolate());
   Local<Value> async_id_value = Number::New(env->isolate(), async_id);
   FatalTryCatch try_catch(env);
   USE(fn->Call(env->context(), Undefined(env->isolate()), 1, &async_id_value));