Refactor texture image filtering

- Support only `Linear` or `Nearest`
- Simplify `Layer` groups
- Move `FilterMethod` to `Image` and `image::Viewer`

renderer/src/lib.rs

@@ -214,8 +214,13 @@ impl<T> crate::core::image::Renderer for Renderer<T> {
         delegate!(self, renderer, renderer.dimensions(handle))
     }
 
-    fn draw(&mut self, handle: crate::core::image::Handle, bounds: Rectangle) {
-        delegate!(self, renderer, renderer.draw(handle, bounds));
+    fn draw(
+        &mut self,
+        handle: crate::core::image::Handle,
+        filter_method: crate::core::image::FilterMethod,
+        bounds: Rectangle,
+    ) {
+        delegate!(self, renderer, renderer.draw(handle, filter_method, bounds));
     }
 }