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`.

graphics/src/image/storage.rs

@@ -0,0 +1,31 @@
+//! Store images.
+use crate::Size;
+
+use std::fmt::Debug;
+
+/// Stores cached image data for use in rendering
+pub trait Storage {
+    /// The type of an [`Entry`] in the [`Storage`].
+    type Entry: Entry;
+
+    /// State provided to upload or remove a [`Self::Entry`].
+    type State<'a>;
+
+    /// Upload the image data of a [`Self::Entry`].
+    fn upload(
+        &mut self,
+        width: u32,
+        height: u32,
+        data: &[u8],
+        state: &mut Self::State<'_>,
+    ) -> Option<Self::Entry>;
+
+    /// Romve a [`Self::Entry`] from the [`Storage`].
+    fn remove(&mut self, entry: &Self::Entry, state: &mut Self::State<'_>);
+}
+
+/// An entry in some [`Storage`],
+pub trait Entry: Debug {
+    /// The [`Size`] of the [`Entry`].
+    fn size(&self) -> Size<u32>;
+}