Migrate to Dokka 0.10.1

[fbenz]

Changes to the Dokka extension:

• Upgrade to Dokka 0.10.1 (see 0.10.1 and 0.10.0)
• Build a test JAR instead of copying the code over. There have been quite some changes in in the test helpers lately.
• Add an integration test to catch potential setup and dependency injection issues. The fix for the DI issue I ran into is the same as in Dokka itself: https://github.com/Kotlin/dokka/blob/de2f32d91fb6f564826ddd7644940452356e2080/core/src/main/kotlin/Formats/FormatDescriptor.kt#L28
• I made sure in the POM file that it has to be build with Java 8.

Example project:

• There is no need for Java 11 dependencies or the Javadoc Doclet in the Gradle build file of the example project.
• reportUndocumented = true is the annoying default and thus I changed it to false.
• I have the checked the resulting documentation and there is no difference.