event sub attribute should error for abstract events

[deltanedas]

i was refactoring some code and wondered why it wasnt working
then i notice its using ref DoAfterEvent args and was specifying the actual type in the subscribe call
god i fucking hate shitcode

the source generator should error if the event type is abstract

[deltanedas]

alternatively SubscribeLocalEvent could check it itself if possible so it would catch manually writing dead code too