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`.

native/src/svg.rs

@@ -1,5 +1,5 @@
 //! Load and draw vector graphics.
-use crate::{Hasher, Rectangle};
+use crate::{Hasher, Rectangle, Size};
 
 use std::borrow::Cow;
 use std::hash::{Hash, Hasher as _};
@@ -82,7 +82,7 @@ impl std::fmt::Debug for Data {
 /// [renderer]: crate::renderer
 pub trait Renderer: crate::Renderer {
     /// Returns the default dimensions of an SVG for the given [`Handle`].
-    fn dimensions(&self, handle: &Handle) -> (u32, u32);
+    fn dimensions(&self, handle: &Handle) -> Size<u32>;
 
     /// Draws an SVG with the given [`Handle`] and inside the provided `bounds`.
     fn draw(&mut self, handle: Handle, bounds: Rectangle);