Add additional forward for clients voting.

[Steell]

Requested by Doobie in IRC.

Should look something like:

UMC_ClientVoted(const String:voteManager[], client, Handle:item);

Due to how this is controlled by the vote manager, it will require a way for the VM to report to core when someone has voted.

The following native is proposed:

UMC_VMReportClientVoted(const String:id[], client, Handle:item);

VoteManagers could probably be rewritten to supply all results to core through this native, rather than tabulating them at the end. This refactor would require a close inspection on how the memory of these handles is managed.

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Placeholder has been added. The forward will fire, but the item Handle will always be INVALID_HANDLE