Update to Minecraft 1.21

By: md_5 <git@md-5.net>

paper-api/src/main/java/org/bukkit/entity/AbstractArrow.java

@@ -17,14 +17,20 @@ public interface AbstractArrow extends Projectile {
      * of the bow that shot it.
      *
      * @return the knockback strength value
+     * @see #getWeapon()
+     * @deprecated a function of the firing weapon
      */
+    @Deprecated
     public int getKnockbackStrength();
 
     /**
      * Sets the knockback strength for an arrow.
      *
      * @param knockbackStrength the knockback strength value
+     * @see #setWeapon(org.bukkit.inventory.ItemStack)
+     * @deprecated a function of the firing weapon
      */
+    @Deprecated
     public void setKnockbackStrength(int knockbackStrength);
 
     /**
@@ -123,7 +129,10 @@ public interface AbstractArrow extends Projectile {
      * Sets if this arrow was shot from a crossbow.
      *
      * @param shotFromCrossbow if shot from a crossbow
+     * @see #setWeapon(org.bukkit.inventory.ItemStack)
+     * @deprecated a function of the firing weapon instead
      */
+    @Deprecated
     public void setShotFromCrossbow(boolean shotFromCrossbow);
 
     /**
@@ -143,6 +152,23 @@ public interface AbstractArrow extends Projectile {
     @ApiStatus.Experimental
     public void setItem(@NotNull ItemStack item);
 
+    /**
+     * Gets the ItemStack which fired this arrow.
+     *
+     * @return The firing ItemStack
+     */
+    @NotNull
+    @ApiStatus.Experimental
+    public ItemStack getWeapon();
+
+    /**
+     * Sets the ItemStack which fired this arrow.
+     *
+     * @param item The firing ItemStack
+     */
+    @ApiStatus.Experimental
+    public void setWeapon(@NotNull ItemStack item);
+
     /**
      * Represents the pickup status of this arrow.
      */