[Move] Restrict types of values that can be fired as events

[awelc]

At this point we throw an error to indicate that an event has been fired with a primitive value as an argument. The proposal here (as discussed with @tnowacki) is t to restrict what value types can be used as arguments when firing events even further, that is to structs defined in the same module that fires the event.

A primitive value event is pretty meaningless as it carries minimal amount of information, but using an arbitrary struct type is also not very informative as it makes it difficult to find out which module was responsible for firing the event.