Remove visually-identical water tiles with different collisions

[wjt]

Currently we have a single water tile with two alternatives. They are visually identical:

The alternatives differ only in the collisions:

• The default tile has a non_walkable_floor shape covering the whole tile
• The first alternative has no non_walkable_floor – it is used for the water below bridges. I've circled the tiles in question in red in the screenshot below.
• The second alternative has a non_walkable_floor shape covering the bottom half of the tile. It is used in a single place in the game: the pontoon in Fray's End. Circled in yellow below.

I have tried and failed to find a good way to make the difference between these three tiles more obvious in the editor. There is no real way to document the purpose of a tile.

Someone on the Godot Discord suggested that we should remove the collision shapes from the water tile and instead have a tileset that is used to block out the level. We would have 3 tiles in the set (currently) whose visual appearance corresponds to the collision shape. Then we would have a TileMapLayer that is used to block out the non-walkable areas of the map. That layer would be hidden.

My other motivation for looking at this is that the void tiles (of which we have 5 variants!) also have a full collision shape, but I want it to be possible to have the void both below the world (to have an island floating above it) and on top of the world (like the invisibility cloak in the Harry Potter films). In the former case the void would need to be walkable, while in the latter it would block movement. There's also one level that has a bridge over the latter kind of void – the closing cutscene of the lorequest. Currently it doesn't matter because in that scene the "player" is just a sprite controlled by an animation player but in general it would be useful to be able to have bridges over the void. I don't want to have to duplicate all 5 voids to have or not have a collision shape.

[manuq]

The idea of decoupling the collisions into a separate, hidden layer is interesting. I think it has pros and cons. It makes a clear separation between the "level blocking" stage (where you don't care about aesthetics) and the "level dressing" stage (where you only care about aesthetics). But the negative aspect is that each time you add eg. a wall tile you'll have to add a wall collision below (if the tile is intended to be a wall).

[wjt]

I think the walls are more self-explanatory. (@jgbourque may not agree, he's talked about using different clifftops for visual effect rather than their collisions, but I think the edges do kind of show you where they are.) I wouldn't remove all collisions, only those for the water (and void) where there is no visual distinction.