Use PNG files for tests and examples

These are much smaller than the previous BMP files

Fixes https://github.com/libsdl-org/SDL/issues/14159

test/testime.c

@@ -1002,7 +1002,7 @@ int main(int argc, char *argv[])
         ctx->window = window;
         ctx->renderer = renderer;
         ctx->rendererID = i;
-        ctx->settings_icon = LoadTexture(renderer, "icon.bmp", true);
+        ctx->settings_icon = LoadTexture(renderer, "icon.png", true);
         if (ctx->settings_icon) {
             ctx->settings_rect.w = (float)ctx->settings_icon->w;
             ctx->settings_rect.h = (float)ctx->settings_icon->h;