Scripting: Expose "Allowed Transformations" properties

[eishiya]

I'd like to write a script that modifies a tileset's "Allowed Transformations", but these properties do not appear to be exposed via the scripting API. Since these properties are shared across the whole tileset, I have to change them frequently based on the Terrains I'm using, and I was hoping to use scripting to automate this.

It would be nice to have these properties exposed, perhaps as Tileset.allowFlipHorizontally, Tileset.allowFlipVertically and Tileset.allowRotate. Edit: It's probably a good idea to expose the "Prefer Untransformed Tiles" setting too.

If #3016 is implemented, then the Tiles' allowed transformations should be exposed similarly. This would allow users to conditionally set these properties en masse.