Fix flickering shadows

[perkinslr]

Changes

For ProjectileCEs which use Graphic_Collection, cache the shadow data and then pick one at random each time the shadow is requested

References

Fixes CombatExtendedRWMod/#1075

Reasoning

This gets simple use cases of Graphic_Flicker or other collections functioning enough (no errors, not obviously wrong).

Alternatives

The shadows are not synchronized with the projectiles. The correct solution would be to add state tracking so the shadow will be synchronized. This could probably be done with a custom random number generator that always gives the same number twice before choosing another randomly. Since the projectile should get drawn, followed by the shadow, this would synchronize them. But it might break other things that use Graphic_Flicker.

We could also subclass Graphic_Flicker, or suggest other mods use a graphic class which doesn't flicker for things which spin.

Testing

Check tests you have performed:

• Compiles without warnings
• Game runs without errors
• (For compatibility patches) ...with and without patched mod loaded
• Playtested a colony (minutes)

[N7Huntsman]

Works.