Add natives to properly use TFCond_TmpDamageBonus

Relevant changes to TF2_AddCondition included:
"Inflictor" changed to "Provider".
Provider is now allowed to be any entity (for instance, dispensers).
Moved actual call to TF2_AddCond to its own function, called by
TF2_AddCondition native (as well as by the TmpDamageBonus natives).
I forgot that we had directly support for props in the Offsets section. I was originally suggesting just putting the prop name in the Keys section and hardcoding the netclass, but this is better.

As for it using GetSendPropOffs, that should work fine for this specific one, but we should fix that to use FindSendPropInfo.