Vendor custom_mouse_cursor 1.1.3 with two patches (upstream is dormant):
- macOS: render at the real devicePixelRatio and set the NSImage point
  size in the plugin, instead of upstream's hardcoded 1.0-DPR clamp
  that shipped blurry cursors on every Retina display.
- All platforms: rasterize icon glyphs at 4x and downscale with
  high-quality filtering so tiny cursor bitmaps get smooth edges.