Make StartupStep AutoCloseable

This commit mames `StartupStep` extend `AutoCloseable` in order to allow
the try/with resources syntax and making the `step.end()` call
transparent.

Closes gh-35277

framework-docs/modules/ROOT/pages/core/beans/context-introduction.adoc

@@ -933,13 +933,12 @@ Java::
 [source,java,indent=0,subs="verbatim,quotes"]
 ----
 	// create a startup step and start recording
-	StartupStep scanPackages = getApplicationStartup().start("spring.context.base-packages.scan");
+	try (StartupStep scanPackages = getApplicationStartup().start("spring.context.base-packages.scan")) {
         // add tagging information to the current step
         scanPackages.tag("packages", () -> Arrays.toString(basePackages));
         // perform the actual phase we're instrumenting
         this.scanner.scan(basePackages);
-	// end the current step
-	scanPackages.end();
+	}
 ----
 
 Kotlin::
@@ -947,13 +946,12 @@ Kotlin::
 [source,kotlin,indent=0,subs="verbatim,quotes"]
 ----
 	// create a startup step and start recording
-	val scanPackages = getApplicationStartup().start("spring.context.base-packages.scan")
+	try (val scanPackages = getApplicationStartup().start("spring.context.base-packages.scan")) {
         // add tagging information to the current step
-	scanPackages.tag("packages", () -> Arrays.toString(basePackages))
+        scanPackages.tag("packages", () -> Arrays.toString(basePackages));
         // perform the actual phase we're instrumenting
-	this.scanner.scan(basePackages)
-	// end the current step
-	scanPackages.end()
+        this.scanner.scan(basePackages);
+	}
 ----
 ======
 

spring-core/src/main/java/org/springframework/core/metrics/StartupStep.java

@@ -36,7 +36,7 @@ import org.jspecify.annotations.Nullable;
  * @author Brian Clozel
  * @since 5.3
  */
-public interface StartupStep {
+public interface StartupStep extends AutoCloseable {
 
 	/**
 	 * Return the name of the startup step.
@@ -83,6 +83,10 @@ public interface StartupStep {
 	 */
 	void end();
 
+	@Override
+	default void close() {
+		this.end();
+	}
 
 	/**
 	 * Immutable collection of {@link Tag}.