New Invader: Catapult

[bilalakil]

The Invader form of the Hammer Stone from #5.

• Moves slowly, quite tanky
• Every two seconds, launches a projectile that stuns a random tower in range for ~2s. (Not sure if this should be a single tower, or area of effect. Needs playtesting 🤔)
• Similar strategic impact to Hammer Stones: target ASAP and/or separate from pack

This implementation can take advantage of Instant Effect Simplification.

• [ ] Create new Catapult enemy with basics implemented (no attack)
  • [ ] Sprite assets created
• [ ] Play special sound on spawn
  • [ ] Sound asset created
• [ ] Play special sound on destruction
  • [ ] Sound asset created
• [ ] Catapult attack animation complete and implemented on cooldown (attack can still do nothing)
  • [ ] Sprite assets created
• [ ] Launch projectile towards tower (can do nothing once reached)
  • [ ] Sprite asset created
    • [ ] If the sprite is asymmetrical then it needs to be rotated according to the direction it's being launched
  • [ ] A small "explosion" occurs when the projectile reaches the tower, including visual and sound components
    • [ ] Explosion VFX created
    • [ ] Sound asset created
• [ ] Projectile stuns tower when reached, using the same stun implementation from #5
• [ ] Introductory level created