chore: Adds an INSTANCE to GoogleSearchTool and LoadArtifactsTool and adds usage example in javadoc

PiperOrigin-RevId: 795552096

Author: Jacksunwei

core/src/main/java/com/google/adk/tools/GoogleSearchTool.java

@@ -31,8 +31,17 @@
  *
  * <p>This tool operates internally within the model and does not require or perform local code
  * execution.
+ *
+ * <p>Usage example in an LlmAgent:
+ *
+ * <pre>{@code
+ * LlmAgent agent = LlmAgent.builder()
+ *     .addTool(GoogleSearchTool.INSTANCE)
+ *     .build();
+ * }</pre>
  */
 public final class GoogleSearchTool extends BaseTool {
+  public static final GoogleSearchTool INSTANCE = new GoogleSearchTool();
 
   public GoogleSearchTool() {
     super("google_search", "google_search");

core/src/main/java/com/google/adk/tools/LoadArtifactsTool.java

@@ -41,8 +41,21 @@
  *
  * <p>This tool informs the model about available artifacts and provides their content when
  * requested by the model through a function call.
+ *
+ * <p>The declaration of this tool is consistent with the Python version. Refer to:
+ * https://github.com/google/adk-python/blob/main/src/google/adk/tools/load_artifacts_tool.py
+ *
+ * <p>Usage example in an LlmAgent:
+ *
+ * <pre>{@code
+ * LlmAgent agent = LlmAgent.builder()
+ *     .addTool(LoadArtifactsTool.INSTANCE)
+ *     .build();
+ * }</pre>
  */
 public final class LoadArtifactsTool extends BaseTool {
+  public static final LoadArtifactsTool INSTANCE = new LoadArtifactsTool();
+
   public LoadArtifactsTool() {
     super("load_artifacts", "Loads the artifacts and adds them to the session.");
   }

core/src/main/java/com/google/adk/utils/ComponentRegistry.java

@@ -96,8 +96,8 @@ private void initializePreWiredEntries() {
     registerAdkAgentClass(ParallelAgent.class);
     registerAdkAgentClass(SequentialAgent.class);
 
-    registerAdkToolInstance("google_search", new GoogleSearchTool());
-    registerAdkToolInstance("load_artifacts", new LoadArtifactsTool());
+    registerAdkToolInstance("google_search", GoogleSearchTool.INSTANCE);
+    registerAdkToolInstance("load_artifacts", LoadArtifactsTool.INSTANCE);
     registerAdkToolInstance("exit_loop", ExitLoopTool.INSTANCE);
 
     registerAdkToolClass(AgentTool.class);