Use Gradle task avoidance

[manuelprinz]

This PR implements task avoidance inside the plugin, because it always configures JaCoCo (and in consequence the test task), even if it is not used in the build. To reproduce, create a build scan with ./gradlew --scan help and check the output as described in the "Troubleshooting" section in the manual. The current release shows 3 created tasks, the version with this PR applied shows 0.

I also took the liberty too add the most recent major versions to the tests and make minor modifications so that the plugin can be used in a composite build with recent Gradle releases. (I needed that for manual testing and creating the build scans.)

Thanks for this great plugin!

[manuelprinz]

Forgot to add the screenshots

Before:

After: