Multi shotgun fix (#8460)

* Multi-barrel shotgun fix

* multi-recoil support

* @Nullable for everything

core/src/mindustry/entities/units/WeaponMount.java

@@ -14,6 +14,8 @@ public class WeaponMount{
     public float rotation;
     /** weapon recoil */
     public float recoil;
+    /** weapon barrel recoil */
+    public @Nullable float[] recoils;
     /** destination rotation; do not modify! */
     public float targetRotation;
     /** current heat, 0 to 1*/
@@ -34,8 +36,10 @@ public class WeaponMount{
     public boolean rotate = false;
     /** extra state for alternating weapons */
     public boolean side;
-    /** total bullets fired from this mount; used for alternating patterns */
+    /** total bullets fired from this mount */
     public int totalShots;
+    /** counter for which barrel bullets have been fired from; used for alternating patterns */
+    public int barrelCounter;
     /** current bullet for continuous weapons */
     public @Nullable Bullet bullet;
     /** sound loop for continuous weapons */