EncounterTrade: don't init Location to -1; keep as default 0 and use that as the pivot for default met location. Move Fateful property to the sub-type that uses it (EncounterTrade4, for Ranch).
Move some EncounterStatic->PKM logic that is per-type to the associated type overloaded methods. Rearrange order of properties to be more consistent with interfaces
Gen3: Initialize some classes without using post-constructor setters. The `init` setter functionality coming in c#9 won't be usable as the net46 runtime/netstandard2 doesn't support it on current previews. Do it this way so we can explicity initialize some required properties rather than apply version on a second iteration.
