Make a strongly typed wrapper for EventListener GC events

In TraceEvent we've got the TraceGC type that provides strong typing for events received via ETW, EventPipe, or Lttng. We should figure out if we can leverage this logic in some way for EventListener or if we should make an alternate strongly typed wrapper. The end goal is to make it as easy as possible for a C# developer to get diagnostic information about the GC occurring within the same process. There is an [alternative path to use EventPipe](https://gist.github.com/noahfalk/935e43bf69e3737f55164ac16f2d2ee6) so we should weigh how much effort to invest here vs. how difficult it is for developers to set that up.