Implement ISteamUGC019

[universal963]

This interface is not public, so header is based on reversing and maybe more checks are needed.

[otavepto]

I'd be skeptical about GetQueryUGCResult() and RequestUGCDetails(), we don't know if in this v19 they started supporting the new mod details struct, or they were still using the older one.
A safer approach would be using the xxx_old() variant like the other older versions.

btw there's a new undocumented ISteamUserStats013 (you can hijack Steam_IsKnownInterface in assembly debugger to get the complete list of supported interfaces) where they simply removed the first function RequestCurrentStats() if you also want to add that 👍

[universal963]

Good point, I've tested again and found out that, for interface ISteamUGC019, GetQueryUGCResult() is now using newer function, just the same as ISteamUGC020, while RequestUGCDetails() is still using older one, which btw is now officially bugged. (for those who care, m_bCachedData of callresult SteamUGCRequestUGCDetailsResult_t is filled with garbage if you are calling it with any interfaces older than ISteamUGC020, and new member m_details.m_ulTotalFilesSize is most probably filled with garbage when calling ISteamUGC020)
And for ISteamUserStats013, I'll wait for next public SDK now, it's a lot easier to check it then.