Simplify internal svg rendering API a little bit

Since there is only one call site now, we can also return the correct
type without inconveniencing any other code.

internal/core/graphics/image.rs

@@ -347,7 +347,7 @@ impl ImageInner {
             #[cfg(feature = "svg")]
             ImageInner::Svg(svg) => {
                 match svg.render(_target_size_for_scalable_source.unwrap_or_default()) {
-                    Ok(b) => Some(SharedImageBuffer::RGBA8Premultiplied(b)),
+                    Ok(b) => Some(b),
                     Err(err) => {
                         eprintln!("Error rendering SVG: {}", err);
                         return None;

internal/core/graphics/image/svg.rs

@@ -6,7 +6,7 @@
 #[cfg(not(target_arch = "wasm32"))]
 use crate::SharedString;
 
-use super::{ImageCacheKey, SharedPixelBuffer};
+use super::{ImageCacheKey, SharedImageBuffer, SharedPixelBuffer};
 
 pub struct ParsedSVG {
     svg_tree: usvg::Tree,
@@ -32,12 +32,10 @@ impl ParsedSVG {
     }
 
     /// Renders the SVG with the specified size.
-    ///
-    /// NOTE: returned Rgba8Pixel buffer has alpha pre-multiplied
     pub fn render(
         &self,
         size: euclid::default::Size2D<u32>,
-    ) -> Result<SharedPixelBuffer<super::Rgba8Pixel>, usvg::Error> {
+    ) -> Result<SharedImageBuffer, usvg::Error> {
         let tree = &self.svg_tree;
         // resvg doesn't support scaling to width/height, just fit to width.
         // FIXME: the fit should actually depends on the image-fit property
@@ -50,7 +48,7 @@ impl ParsedSVG {
                 .ok_or(usvg::Error::InvalidSize)?;
         resvg::render(tree, fit, Default::default(), skia_buffer)
             .ok_or(usvg::Error::InvalidSize)?;
-        Ok(buffer)
+        Ok(SharedImageBuffer::RGBA8Premultiplied(buffer))
     }
 }