Migration to JUnit 5 - avoid using AbstractMojoTestCase

[slawekjaranowski]

• Migration finished
• bump plugin-testing to 3.5.0
• cleanups after parent

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[sparsick]

Also, please check if the following dependencies are still necessary:

    <dependency>
      <!-- support for JUnit 4 -->
      <groupId>org.junit.vintage</groupId>
      <artifactId>junit-vintage-engine</artifactId>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.13.2</version>
      <scope>test</scope>
    </dependency>

Should we rename the test classes, so that they have a Test suffix?

[slawekjaranowski]

Should we rename the test classes, so that they have a Test suffix?

There are many tests to rename .... we can do it in separate PR