Issue 4127 - [emscripten] Convert subscription classes to C++ - Part 1

compiled/subscription/DownloadableSubscription.h

+#pragma once
+
+#include "Subscription.h"
+
+class DownloadableSubscription : public Subscription
+{
+public:
+  explicit DownloadableSubscription(const String& id);
+
+  SUBSCRIPTION_PROPERTY(bool, mFixedTitle, GetFixedTitle, SetFixedTitle);
+  SUBSCRIPTION_STRING_PROPERTY(mHomepage, GetHomepage, SetHomepage);
+  SUBSCRIPTION_PROPERTY(double, mLastCheck, GetLastCheck, SetLastCheck);
+  SUBSCRIPTION_PROPERTY(double, mHardExpiration, GetHardExpiration, SetHardExpiration);
+  SUBSCRIPTION_PROPERTY(double, mSoftExpiration, GetSoftExpiration, SetSoftExpiration);
+  SUBSCRIPTION_PROPERTY(double, mLastDownload, GetLastDownload, SetLastDownload);
+  SUBSCRIPTION_STRING_PROPERTY(mDownloadStatus, GetDownloadStatus, SetDownloadStatus);
+  SUBSCRIPTION_PROPERTY(double, mLastSuccess, GetLastSuccess, SetLastSuccess);
+  SUBSCRIPTION_PROPERTY(int, mErrorCount, GetErrorCount, SetErrorCount);
+  SUBSCRIPTION_PROPERTY(double, mDataRevision, GetDataRevision, SetDataRevision);
+  SUBSCRIPTION_STRING_PROPERTY(mRequiredVersion, GetRequiredVersion, SetRequiredVersion);
+  SUBSCRIPTION_PROPERTY(int, mDownloadCount, GetDownloadCount, SetDownloadCount);
+
+  EMSCRIPTEN_KEEPALIVE OwnedString Serialize() const;
+};