Document app.pixelColor.tile, tileI and tileF methods

Methods required to decompose and compose tile map entry indices and flipping flags would help people write custom tile map exports. Constants such as `TILE_XFLIP`, `TILE_XFLIP`, `TILE_DFLIP` would also be useful.

This applies to cases where it'd be impractical for Aseprite to cover all the different tile map formats across game engines. For example, the most recent question I've seen: https://www.reddit.com/r/aseprite/comments/1nbfzer/lua_script_for_exporting_tilemap_with_mirrored/ .

More documentation than a brief listing of methods and constants would help. Since Aseprite's use of flipping flags is similar to Tiled, see https://doc.mapeditor.org/en/stable/reference/global-tile-ids/#gid-tile-flipping as an example. Relevant code internal to Aseprite would be

https://github.com/aseprite/aseprite/blob/main/src/doc/tile.h

https://github.com/aseprite/aseprite/blob/main/src/app/script/pixel_color_object.cpp#L93