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`.

glow/src/image/storage.rs

@@ -0,0 +1,78 @@
+use iced_graphics::image;
+use iced_graphics::Size;
+
+use glow::HasContext;
+
+#[derive(Debug, Default)]
+pub struct Storage;
+
+impl image::Storage for Storage {
+    type Entry = Entry;
+    type State<'a> = &'a glow::Context;
+
+    fn upload(
+        &mut self,
+        width: u32,
+        height: u32,
+        data: &[u8],
+        gl: &mut &glow::Context,
+    ) -> Option<Self::Entry> {
+        unsafe {
+            let texture = gl.create_texture().expect("create texture");
+            gl.bind_texture(glow::TEXTURE_2D, Some(texture));
+            gl.tex_image_2d(
+                glow::TEXTURE_2D,
+                0,
+                glow::SRGB8_ALPHA8 as i32,
+                width as i32,
+                height as i32,
+                0,
+                glow::BGRA,
+                glow::UNSIGNED_BYTE,
+                Some(data),
+            );
+            gl.tex_parameter_i32(
+                glow::TEXTURE_2D,
+                glow::TEXTURE_WRAP_S,
+                glow::CLAMP_TO_EDGE as _,
+            );
+            gl.tex_parameter_i32(
+                glow::TEXTURE_2D,
+                glow::TEXTURE_WRAP_T,
+                glow::CLAMP_TO_EDGE as _,
+            );
+            gl.tex_parameter_i32(
+                glow::TEXTURE_2D,
+                glow::TEXTURE_MIN_FILTER,
+                glow::LINEAR as _,
+            );
+            gl.tex_parameter_i32(
+                glow::TEXTURE_2D,
+                glow::TEXTURE_MAG_FILTER,
+                glow::LINEAR as _,
+            );
+            gl.bind_texture(glow::TEXTURE_2D, None);
+
+            Some(Entry {
+                size: Size::new(width, height),
+                texture,
+            })
+        }
+    }
+
+    fn remove(&mut self, entry: &Entry, gl: &mut &glow::Context) {
+        unsafe { gl.delete_texture(entry.texture) }
+    }
+}
+
+#[derive(Debug)]
+pub struct Entry {
+    size: Size<u32>,
+    pub(super) texture: glow::NativeTexture,
+}
+
+impl image::storage::Entry for Entry {
+    fn size(&self) -> Size<u32> {
+        self.size
+    }
+}