Expand PotionMeta Api to allow getting effective potion colour and effects (#12390)

paper-api/src/main/java/org/bukkit/inventory/meta/PotionMeta.java

@@ -8,6 +8,7 @@ import org.bukkit.potion.PotionEffectType;
 import org.bukkit.potion.PotionType;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
+import org.jetbrains.annotations.Unmodifiable;
 
 /**
  * Represents a potion or item that can have custom effects.
@@ -74,6 +75,16 @@ public interface PotionMeta extends ItemMeta {
     @NotNull
     List<PotionEffect> getCustomEffects();
 
+    /**
+     * All effects that this potion meta holds.
+     * <p>
+     * This is a combination of the base potion type and any custom effects.
+     *
+     * @return an unmodifiable list of all effects.
+     */
+    @NotNull
+    @Unmodifiable List<PotionEffect> getAllEffects();
+
     /**
      * Adds a custom potion effect to this potion.
      *
@@ -146,6 +157,16 @@ public interface PotionMeta extends ItemMeta {
      */
     void setColor(@Nullable Color color);
 
+    /**
+     * Computes the effective colour of this potion meta.
+     * <p>
+     * This blends all custom effects, or uses a default fallback color.
+     *
+     * @return the effective potion color
+     */
+    @NotNull
+    Color computeEffectiveColor();
+
     /**
      * Checks for existence of a custom potion name translation suffix.
      *