Document @MethodSource as use case for @TestInstance per-class lifecycle

This commit documents another use case for TestInstace.PER_CLASS in Kotlin,
namely, using a regular simple class method as a factory method for @MethodSource
(which is used for parameterized tests).

Closes: #3219

Author: mahozad

documentation/src/docs/asciidoc/user-guide/writing-tests.adoc

@@ -751,8 +751,8 @@ NOTE: Beginning with Java 16, `@BeforeAll` and `@AfterAll` methods can be declar
 `static` in `@Nested` test classes.
 
 If you are authoring tests using the Kotlin programming language, you may also find it
-easier to implement `@BeforeAll` and `@AfterAll` methods by switching to the "per-class"
-test instance lifecycle mode.
+easier to implement `@BeforeAll` and `@AfterAll` methods and also factory methods for
+`@MethodSource` by switching to the "per-class" test instance lifecycle mode.
 
 [[writing-tests-test-instance-lifecycle-changing-default]]
 ==== Changing the Default Test Instance Lifecycle

junit-jupiter-api/src/main/java/org/junit/jupiter/api/TestInstance.java

@@ -51,7 +51,8 @@
  * <li>Declaration of {@code @BeforeAll} and {@code @AfterAll} on interface
  * {@code default} methods.</li>
  * <li>Simplified declaration of non-static {@code @BeforeAll} and {@code @AfterAll}
- * methods in test classes implemented with the Kotlin programming language.</li>
+ * methods and also factory methods for {@code @MethodSource} in test classes
+ * implemented with the Kotlin programming language.</li>
  * </ul>
  *
  * <p>{@code @TestInstance} may also be used as a meta-annotation in order to