reintroduce and deprecate ObjectUtils.merge

Signed-off-by: Tobias Ibounig <tobias.ibounig@dynatrace.com>

Author: tobias-ibounig-dt

src/main/java/dev/openfeature/sdk/HookSupport.java

@@ -2,7 +2,6 @@
 
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.List;
 import java.util.Optional;
 import lombok.extern.slf4j.Slf4j;

src/main/java/dev/openfeature/sdk/internal/ObjectUtils.java

@@ -1,5 +1,7 @@
 package dev.openfeature.sdk.internal;
 
+import java.util.ArrayList;
+import java.util.Collection;
 import java.util.List;
 import java.util.Map;
 import java.util.function.Supplier;
@@ -54,4 +56,22 @@ public static <T> T defaultIfNull(T source, Supplier<T> defaultValue) {
         }
         return source;
     }
+
+    /**
+     * Concatenate a bunch of lists.
+     *
+     * @param sources bunch of lists.
+     * @param <T>     list type
+     * @return resulting object
+     * @deprecated Not used in the project anymore. This method will be removed in a future release.
+     */
+    @Deprecated(forRemoval = true)
+    @SafeVarargs
+    public static <T> List<T> merge(Collection<T>... sources) {
+        List<T> merged = new ArrayList<>();
+        for (Collection<T> source : sources) {
+            merged.addAll(source);
+        }
+        return merged;
+    }
 }