Move TileMapLayer to its own files

[groud]

As I mentioned in this proposal, I'd like to move TileMap layers to their own node. This fits the

I prefer to go there step by step. This first PR moves TileMap layer to another file.

The next steps would be:

• Change TileMap layers to be used as an internal nodes for the TileMap node (and make sure everything works).
• Implement a TileMapGroup node, that would constraint its child TileMapLayer nodes to use a given TileSet, and to keep their transform. It should have a very simple API. Keep TileMapGroup node private for now.
• Make TileMap expand the TileMapGroup node API.
• To ensure compatibility, implement a tool to transform the TileMap node into the (TileMapGroup + Children TileMap layers).
• At the same time:
  • expose the TileMapLayer node.
  • expose the TileMapGroup node.
  • Change the editor to edit TileMapLayer directly (and, for simplicity of the implementation, probably disables it for the TileMap node. That kind of forces people to move the to new workflow by using the auto-conversion, but it's probably acceptable IMO)

Basically, the TileMap node could become the equivalent of (TileMapGroup + Children TileMap layers), with layers being internal nodes instead of being explicit ones.

[AThousandShips]

I'm a bit concerned by the circular inclusion, can this not be handled in any other way?

[groud]

I'm a bit concerned by the circular inclusion, can this not be handled in any other way?

I thought there was not, but I managed to solve it.

[YuriSizov]

Needs a rebase and we can merge it soon if it unblocks your further work.

[groud]

Needs a rebase and we can merge it soon if it unblocks your further work.

I'll rebase once #84660 is merged, to avoid conflicts.

[YuriSizov]

@groud You should be able to rebase now!

[akien-mga]

New Year's rebase poke ;)

[groud]

New Year's rebase poke ;)

Done!

[akien-mga]

Thanks!