feat(flex_row): reorderable rows with shadow constant gated (squashed)

Squash of 2 yoda commits:
- 7dd0ee83 feat: reorderable flex row
- b1b8203a fix: gate reorderable flex row shadow constant

src/widget/reorderable_flex_row/widget.rs

@@ -21,6 +21,7 @@ use std::time::{Duration, Instant};
 const DEFAULT_ANIMATION_DURATION: Duration = Duration::from_millis(180);
 const DEFAULT_DRAG_LIFT: f32 = 10.0;
 const DEFAULT_DRAG_THRESHOLD: f32 = 6.0;
+#[cfg(feature = "wgpu")]
 const SHADOW_BLUR_RADIUS: f32 = 20.0;
 const POSITION_EPSILON: f32 = 0.5;