fix: Leave context after Runtime::PrepareV8Runtime()

In PrepareV8Runtime() we enter the context but never leave it. This is
mostly harmless but fails a DCHECK because when we leave the scope of the
Locker, there is not supposed to be an entered context.

test-app/runtime/src/main/cpp/Runtime.cpp

@@ -588,7 +588,7 @@ Isolate* Runtime::PrepareV8Runtime(const string& filesPath, const string& native
 
     auto global = context->Global();
 
-    context->Enter();
+    v8::Context::Scope contextScope{context};
 
     m_objectManager->Init(isolate);