Refactor Build method return type in CacheDependencyKeyBuilder

This commit updates the `Build` method in the `CacheDependencyKeyBuilder` class, changing its return type from `IEnumerable<string>` to `string[]`. This change necessitates updating the method's implementation to return `_keys.ToArray()` to match the new return type. The modification aims to improve performance, ensure type consistency, and align with other parts of the codebase expecting an array return type. Other methods, including `AddPath` and `ForContentItem`, remain unchanged, maintaining their roles in configuring cache dependency keys.

src/XperienceCommunity.OutputCache/CacheDependencyKeyBuilder.cs

@@ -52,9 +52,9 @@ public CacheDependencyKeyBuilder AddPath(string path)
             return AddKey($"bypath|{path}");
         }
 
-        public IEnumerable<string> Build()
+        public string[] Build()
         {
-            return _keys;
+            return _keys.ToArray();
         }
 
         public CacheDependencyKeyBuilder ForContentItem()