Rename internal OutputCapture classes

Rename the internal versions of OutputCapture to prevent accidental
import.

See gh-5492

spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/InternalOutputCapture.java

@@ -30,7 +30,7 @@ import org.junit.runners.model.Statement;
  *
  * @author Phillip Webb
  */
-public class OutputCapture implements TestRule {
+class InternalOutputCapture implements TestRule {
 
 	private CaptureOutputStream captureOut;
 

spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/PropertiesLauncherTests.java

@@ -43,7 +43,7 @@ import static org.assertj.core.api.Assertions.assertThat;
 public class PropertiesLauncherTests {
 
 	@Rule
-	public OutputCapture output = new OutputCapture();
+	public InternalOutputCapture output = new InternalOutputCapture();
 
 	@Before
 	public void setup() throws IOException {