Introduce trySetSkipped and its variants

Author: Yeregorix

src/main/java/org/spongepowered/api/event/cause/entity/damage/DamageStep.java

@@ -69,6 +69,58 @@ public interface DamageStep {
      */
     void setSkipped(boolean skipped);
 
+    /**
+     * Sets whether this step is skipped.
+     * This has no effect if the step has already finished.
+     *
+     * @see #isSkipped()
+     */
+    default void trySetSkipped(boolean skipped) {
+        if (this.damageAfterSelf().isEmpty()) {
+            this.setSkipped(skipped);
+        }
+    }
+
+    /**
+     * Sets whether the children before this step are skipped.
+     * This has no effect on steps already finished.
+     *
+     * @see #isSkipped()
+     */
+    default void trySetChildrenBeforeSkipped(boolean skipped) {
+        if (this.damageBeforeSelf().isEmpty()) {
+            for (DamageStep child : this.childrenBefore()) {
+                child.trySetSkipped(skipped);
+            }
+        }
+    }
+
+    /**
+     * Sets whether the children after this step are skipped.
+     * This has no effect on steps already finished.
+     *
+     * @see #isSkipped()
+     */
+    default void trySetChildrenAfterSkipped(boolean skipped) {
+        if (this.damageAfterChildren().isEmpty()) {
+            for (DamageStep child : this.childrenAfter()) {
+                child.trySetSkipped(skipped);
+            }
+        }
+    }
+
+    /**
+     * Sets whether this step and its children are skipped.
+     * This has no effect on steps already finished.
+     *
+     * @see #isSkipped()
+     */
+    default void trySetAllSkipped(boolean skipped) {
+        this.trySetChildrenBeforeSkipped(skipped);
+        this.trySetSkipped(skipped);
+        this.trySetChildrenAfterSkipped(skipped);
+    }
+
     /**
      * Skips this step.
      *