Playtime credit must be consumed and turned into item drops by your game. Only item
definitions which are marked as "playtime item generators" can be spawned. The call
will return an empty result set if there is not enough playtime credit for a drop.
Your game should call TriggerItemDrop at an appropriate time for the user to receive
new items, such as between rounds or while the player is dead. Note that players who
hack their clients could modify the value of "dropListDefinition", so do not use it
to directly control rarity.
See your Steamworks configuration to set playtime drop rates for individual itemdefs.
The client library will suppress too-frequent calls to this method.
