Function render_icon_data 

pub fn render_icon_data(
    painter: &Painter,
    rect: Rect,
    vertices: &[(f32, f32)],
    indices: &[u32],
    viewbox_width: f32,
    viewbox_height: f32,
    color: Color32,
)

Render icon geometry to an egui painter.

Low-level function that takes raw vertex/index slices. Both render_icon and OwnedIconData::render delegate to this.