gpui: Rasterize parsed SVGs at exact sizes (#62770)

# Objective

Allow callers to rasterize parsed SVGs at exact device-pixel dimensions.

## Solution

Add `SvgSize::ExactSize` and accept `SvgSize` in `render_parsed`.
Existing scale-factor calls retain their 2× rasterization behavior.
`SvgSize::Size` continues to preserve the SVG aspect ratio.

Release Notes:

- N/A
03c9c4e707Ben Kunkle committed on 8/18/2026, 2:13:27 PM· committed by GitHubparenta7d7415
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