Allow loading a TSX file from Python plugins

[Ruin0x11]

This pull request adds a method to the Python API, loadSharedTilesetFromTsx, which allows loading an existing TSX file as a tileset.

The use case I'm thinking of is embedding the path to a specific version of a TSX in a map format, then attempting to resolve it when the map is loaded in Tiled, and sharing the same TSX across multiple map files. The data system we have may support several groups of tiles loaded from outside sources like mods which can be enabled and disabled, so I was thinking about pregenerating a TSX for a single supported configuration of enabled/disabled mods, caching the tile images somewhere, and allowing them to be used in the editor.

[bjorn]

Thanks for your patch! It definitely makes sense for the Python plugins to be able to load external tilesets while loading a map.

Since generally we want to avoid loading the same tileset multiple times, there is the TilesetManager through which tilesets are loaded. Also, I think it would make sense for this function to work with any supported tileset format rather than just TSX. So, what about renaming this to simply loadTileset and implementing it based on TilesetManager::loadTileset?

[Ruin0x11]

Yes, that makes sense. It also prevents the behavior where the same tileset shows up in the editor multiple times.

[bjorn]

Thanks!