Gets a tile at the given tile coordinates from the given layer.
X position to get the tile from (given in tile units, not pixels).
Y position to get the tile from (given in tile units, not pixels).
If true getTile won't return null for empty tiles, but a Tile object with an index of -1.
The Tilemap Layer to act upon.
The tile at the given coordinates or null if no tile was found or the coordinates were invalid.