Add terrain-based footstep sound system

[Leonardo-UTP]

Description

Adds support for terrain-based footstep sounds.

The player can now detect the material of the tile beneath them using a TileSet Custom Data Layer named material. When a footstep is triggered by the walk animation, the corresponding sound configured for that material is played.

If no sound is configured for the detected material, the existing default footstep sound is used as a fallback.

Changes

• Added a FootstepSound component to the player.
• Added terrain material detection using TileSet Custom Data.
• Added configurable sounds for different terrain materials.
• Connected terrain detection to the footstep frames of the walk animation.
• Preserved the existing footstep sound as the default fallback.

Fixes #1095

[github-actions]

Play this branch at https://play.threadbare.game/branches/Leonardo-UTP/issue-1095-footstep-sounds/.

(This launches the game from the start, not directly at the change(s) in this pull request.)