Drag cursor for FeathersNumberInput is overbearing

The feathers number input widget uses the standard winit `ColResize` cursor when dragging. This cursor is a little too big and covers too much - it's hard to see the number value.

Unfortunately, winit's collection of standard cursors don't provide very many shapes. Although it has all of the enum variants of the CSS cursors, many of those variants map to the same icon.

The CSS "EWResize" is smaller and less intrusive than the "ColResize" cursor, but in winit those map to the same cursor image.

The only way to solve this is to use a custom cursor image. This will need to be an embedded asset (because Feathers cannot load assets from disk).

Start by locating the FeathersNumberInput cursor handling and existing embedded asset patterns. Compare the current winit ColResize cursor with the proposed custom cursor while dragging, and verify that the number value remains visible and the widget still behaves correctly.

Written by the indexing model from the issue text.