Refactor some image traits a bit

- Use `Size<u32>` were applicable.
- Rename `TextureStore` to `image::Storage`.
- Rename `TextureStoreEntry` to `image::storage::Entry`.
- Wire up `viewport_dimensions` to `iced_glow` for `Svg`.

wgpu/src/image/atlas/entry.rs

@@ -1,17 +1,19 @@
 use crate::image::atlas;
-use iced_graphics::image::TextureStoreEntry;
+
+use iced_graphics::image;
+use iced_graphics::Size;
 
 #[derive(Debug)]
 pub enum Entry {
     Contiguous(atlas::Allocation),
     Fragmented {
-        size: (u32, u32),
+        size: Size<u32>,
         fragments: Vec<Fragment>,
     },
 }
 
-impl TextureStoreEntry for Entry {
-    fn size(&self) -> (u32, u32) {
+impl image::storage::Entry for Entry {
+    fn size(&self) -> Size<u32> {
         match self {
             Entry::Contiguous(allocation) => allocation.size(),
             Entry::Fragmented { size, .. } => *size,