Add FlxTilemap.loadMapFromImage()

[Gama11]

...using FlxStringUtil.imageToCSV(). Suggested by @SeiferTim.

[Gama11]

Perhaps fromGraphic would be better for consistency with FlxSprite functions.

[Gama11]

No breaking changes necessary here, moving this to 4.1.0.

[Beeblerox]

this method could look like this:

/**
     * Load the tilemap with image data and a tile graphic. 
     * Black pixels are flagged as 'solid' by default, non-black pixels are set as non-colliding. Black pixels must be PURE BLACK.
     * @param   MapGraphic      The image you want to use as a source of map data, where each pixel is a tile (or more than one tile if you change Scale's default value). Preferably black and white.
     * @param   Invert          Load white pixels as solid instead.
     * @param   Scale           Default is 1. Scale of 2 means each pixel forms a 2x2 block of tiles, and so on.
     * @param   ColorMap        An array of color values (alpha values are ignored) in the order they're intended to be assigned as indices
     * @param   TileGraphic     All the tiles you want to use, arranged in a strip corresponding to the numbers in MapData.
     * @param   TileWidth       The width of your tiles (e.g. 8) - defaults to height of the tile graphic if unspecified.
     * @param   TileHeight      The height of your tiles (e.g. 8) - defaults to width if unspecified.
     * @param   AutoTile        Whether to load the map using an automatic tile placement algorithm (requires 16 tiles!).
     *                          Setting this to either AUTO or ALT will override any values you put for StartingIndex, DrawIndex, or CollideIndex.
     * @param   StartingIndex   Used to sort of insert empty tiles in front of the provided graphic.
     *                          Default is 0, usually safest ot leave it at that.  Ignored if AutoTile is set.
     * @param   DrawIndex       Initializes all tile objects equal to and after this index as visible.
     *                          Default value is 1. Ignored if AutoTile is set.
     * @param   CollideIndex    Initializes all tile objects equal to and after this index as allowCollisions = ANY.
     *                          Default value is 1.  Ignored if AutoTile is set.  
     *                          Can override and customize per-tile-type collision behavior using setTileProperties().
     * @return  A reference to this instance of FlxTilemap, for chaining as usual :)
     */
    public function loadMapFromGraphic(MapGraphic:FlxGraphicSource, Invert:Bool = false, Scale:Int = 1, ?ColorMap:Array<FlxColor>, TileGraphic:FlxTilemapGraphicAsset, TileWidth:Int = 0, TileHeight:Int = 0, ?AutoTile:FlxTilemapAutoTiling, StartingIndex:Int = 0, DrawIndex:Int = 1, CollideIndex:Int = 1)
    {
        var mapBitmap:BitmapData = FlxAssets.resolveBitmapData(MapGraphic);
        var mapData:String = FlxStringUtil.bitmapToCSV(mapBitmap, Invert, Scale, ColorMap);
        return loadMapFromCSV(mapData, TileGraphic, TileWidth, TileHeight, AutoTile, StartingIndex, DrawIndex, CollideIndex);
    }