Creatures above cast shadows onto tiles below

[Rewryte]

Summary

Features "Creatures above cast shadows onto tiles below"

Purpose of change

Creatures above the z-level of the player can be difficult to detect due to the lack of visual indications of their presence.
Fixes #66657

Describe the solution

Make creatures cast shadows unto tiles below. Image used for the shadow is determined by each tileset via the new shadow sprite id. The hostility indicator will also be drawn when applicable. Naturally, this feature will not be functional until a shadow sprite is assigned to the tilesets and the next tileset update takes place. I will work on that unless someone else wants to.

A simpler version is used in curses which mimics how critters below the current z-level are currently drawn. Because the "critter above" indicator has the potential to obscure the underlying tile, both the "critter above" and "critter below" indicator were made to blink. These are affected by the "Blinking effects speed" setting.

Describe alternatives you've considered

Testing

Builds ok in both tiles and curses.
Tested in both isometric and non-isometric mode by assigning a shadow sprite using a mod
Both shadow and hostility indicators are drawn correctly.
Performance impact is negligible.

Additional context

[GuardianDll]

I guess it should resolve #66657

[Rewryte]

I guess it should resolve #66657

Thanks. Updated main comment.

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[RenechCDDA]

I hope you don't mind some questions

How does it handle if a creature(with its own sprite) is occupying the tile where the shadow would be placed? (Looking at the changes, seems it just doesn't draw the shadow?)

What if the creature on z=0 does not have a sprite defined (or is using ASCII fallback), does it still cancel out drawing the shadow sprite?

Does it draw the shadow if the shadow would be placed on an 'impassable' tile (e.g. the walled edge of a building)?

[Rewryte]

How does it handle if a creature(with its own sprite) is occupying the tile where the shadow would be placed? (Looking at the changes, seems it just doesn't draw the shadow?)

Yup. Tilesets like Ultica give creatures their own shadows so I didn't think it necessary.

What if the creature on z=0 does not have a sprite defined (or is using ASCII fallback), does it still cancel out drawing the shadow sprite?

Any draw function with a fallback should still return true which should stop the shadow drawing. If nothing is drawn, such as in the case of an invisible creature, then the shadow function will run.

Does it draw the shadow if the shadow would be placed on an 'impassable' tile (e.g. the walled edge of a building)?

Nope. Both walls and the ceiling above them should return true on dont_draw_lower_floor. This stops the function from scanning for creatures.