feat: Adjusted the hitbox coordinates of where the stones should be dropped (FM-266).

[bernhardccodev]

Changes

• Moved the handling if the stones dropped on the correct coordinates from gameplay-scene.ts to monster.ts.

How to test

• Run locally, then start the game.
• Select any level and during the gameplay, dropping of stones should be withing or very close to the monster's face.
• Repeat this process on different screen sizes.

Ref: FM-266