Implement being able to drop through soft platforms (#64)

Reviewed-on: #64
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/fighter/surface.rs

@@ -57,6 +57,14 @@ impl FighterSurfaceState {
         *self = Self::Grounded { line_id };
     }
 
+    pub fn clear_polygon_ignore(&mut self, polygon: usize) {
+        let Self::Airborne { ignored_polys, .. } = self else {
+            return;
+        };
+
+        ignored_polys.retain(|element| element.polygon != polygon);
+    }
+    
     pub fn ignore_polygon(&mut self, polygon: usize, duration_frames: u32) {
         let Self::Airborne { ignored_polys, .. } = self else {
             return;