Add GenImageGradientSquare (#3077)

* Add GenImageGradientSquare to allow square gradients

* Fix GenImageGradientSquare and add to textures_image_generation example

* Remove params from GenImageGradientSquare

src/raylib.h

@@ -1241,6 +1241,7 @@ RLAPI bool ExportImageAsCode(Image image, const char *fileName);
 RLAPI Image GenImageColor(int width, int height, Color color);                                           // Generate image: plain color
 RLAPI Image GenImageGradientLinear(int width, int height, int direction, Color start, Color end);        // Generate image: linear gradient, direction in degrees [0..360], 0=Vertical gradient
 RLAPI Image GenImageGradientRadial(int width, int height, float density, Color inner, Color outer);      // Generate image: radial gradient
+RLAPI Image GenImageGradientSquare(int width, int height, float density, Color inner, Color outer);      // Generate image: square gradient
 RLAPI Image GenImageChecked(int width, int height, int checksX, int checksY, Color col1, Color col2);    // Generate image: checked
 RLAPI Image GenImageWhiteNoise(int width, int height, float factor);                                     // Generate image: white noise
 RLAPI Image GenImagePerlinNoise(int width, int height, int offsetX, int offsetY, float scale);           // Generate image: perlin noise