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.
Actually, you can avoid all of this by using the clearer:
```csharp
var sequence = Info.DeathSequence;
if (Info.UseDeathTypeSuffix)
	sequence += e.Warhead.DeathType;

var palette = Info.DeathSequencePalette;
if (Info.DeathPaletteIsPlayerPalette)
	palette += self.Owner.InternalName;

SpawnDeathAnimation(self, sequence, palette);
```