gpui: Render SVGs at 2x size when rendered in an img (#24332)

This PR adjusts the rendering of SVGs when used with the `img` element
such that they are rendered at 2x their displayed size.

This results in much crisper icons for icons loaded by icon themes:

<img width="1136" alt="Screenshot 2025-02-05 at 7 39 48 PM"
src="https://github.com/user-attachments/assets/47d1fcee-c54d-4717-8fca-9b9d2bc8da9a"
/>

<img width="1136" alt="Screenshot 2025-02-05 at 7 40 01 PM"
src="https://github.com/user-attachments/assets/3061157c-8c88-41c1-a5dc-83ef9cd341cb"
/>

Release Notes:

- Improved the resolution of icons rendered by icon themes.

crates/gpui/src/svg_renderer.rs

@@ -3,6 +3,9 @@ use anyhow::anyhow;
 use resvg::tiny_skia::Pixmap;
 use std::{hash::Hash, sync::Arc};
 
+/// When rendering SVGs, we render them at twice the size to get a higher-quality result.
+pub const SMOOTH_SVG_SCALE_FACTOR: f32 = 2.;
+
 #[derive(Clone, PartialEq, Hash, Eq)]
 pub(crate) struct RenderSvgParams {
     pub(crate) path: SharedString,