Added WithDeathAnimation

Deprecated RenderInfantry's SpawnsCorpse logic, renamed CrushableInfantry to Crushable (it can now be used to make other actors crushable too, afterall).

Closes #6375.

This can be used to replace DeadBuildingState, too, once #6389 is fixed.

For corpses rather than death animations, read the comments on #4163 about using LeavesHusk for that.
These two ifs can be merged.  You may also want to use `crushOwner.IsAlliedWith(self.Owner)`, but that's something that we are really inconsistent about in the code so it could go either way.