Enrich assertInstanceOf failure with cause

[vy]

As agreed in this discussion, enrich assertInstanceOf failure with cause.

jshell demonstration

$ jshell --class-path opentest4j-1.3.0.jar:junit-platform-commons-6.1.0-SNAPSHOT.jar:junit-jupiter-api-6.1.0-SNAPSHOT.jar
|  Welcome to JShell -- Version 25
|  For an introduction type: /help intro

jshell> org.junit.jupiter.api.Assertions.assertInstanceOf(RuntimeException.class, new java.io.IOException())
|  Exception org.opentest4j.AssertionFailedError: Unexpected type, expected: <java.lang.RuntimeException> but was: <java.io.IOException>
|        at AssertionFailureBuilder.build (AssertionFailureBuilder.java:158)
|        at AssertionFailureBuilder.buildAndThrow (AssertionFailureBuilder.java:139)
|        at AssertInstanceOf.assertInstanceOf (AssertInstanceOf.java:59)
|        at AssertInstanceOf.assertInstanceOf (AssertInstanceOf.java:35)
|        at Assertions.assertInstanceOf (Assertions.java:3688)
|        at (#1:1)
|  Caused by: java.io.IOException
|        ...

Note the Caused by: java.io.IOException at the end, which is added by this PR.

[marcphilipp]

Thanks, @vy! 👍