Rerasterize SVGs when resized and refactor a bit

wgpu/src/renderer/widget/svg.rs

@@ -0,0 +1,22 @@
+use crate::{Primitive, Renderer};
+use iced_native::{svg, Layout, MouseCursor};
+
+impl svg::Renderer for Renderer {
+    fn dimensions(&self, handle: &svg::Handle) -> (u32, u32) {
+        self.image_pipeline.viewport_dimensions(handle)
+    }
+
+    fn draw(
+        &mut self,
+        handle: svg::Handle,
+        layout: Layout<'_>,
+    ) -> Self::Output {
+        (
+            Primitive::Svg {
+                handle,
+                bounds: layout.bounds(),
+            },
+            MouseCursor::OutOfBounds,
+        )
+    }
+}