Adds an OnPlayerRunCmdPre forward in order for plugins to be able to hook OnPlayerRunCmd with the guarantee that none of the parameters have been modified by other plugins. As such, OnPlayerRunCmdPre's parameters cannot be modified and are read-only.
Plugins that wish to use OnPlayerRunCmdPre can maintain backwards compatibility with SourceMod 1.10 by falling back to OnPlayerRunCmd if the Pre variant was never fired.
