fix #2365 about leaderboards functions

[YoungHypo]

A Solution for #2365 :

Description

Create std::list<LeaderboardRequest> LBRequestList for all download or upload leaderboards requests, and a LeaderboardRequest structure object to store the relevant parameters for the calls.

Example:

Take the steam_download_scores function leaderboards.cpp as an example, first add the leaderboard request of download_scores func to LBRequestList. When find_leaderboard func completes the find operation, the list will release the download request for execution. Therefore, the "download" of the leaderboard entry always follows the operation of finding the leaderboard, and the two remain synchronized.
@k0T0z

[k0T0z]

Is this PR ready for review?

[YoungHypo]

yes, I‘ve referred to GameMaker's implementation and I think it can be checked. thanks for your help.

[k0T0z]

Interesting! I didn't know we could access GMS Steamworks' implementation, where did you get that?

[YoungHypo]

Sorry, please forgive my inaccurate expression. It's not about accessing GMS, but learning the code of GMS's steamwork extension. I mean the GMEXT-Steamworks. It was your words in the discord group that inspired me.