Annotation ComponentTesterPackages should be inheritable

[stefanuebe]

We want to define a set of custom testers for a huge set of UI Unit tests. Each of those UI Unit tests is going to extend from a custom base class, that itself extends the Vaadin ui unit base class. This custom class shall also be annotated with the custom tester annotation.

Currently, this is not possible since the annotation ComponentTesterPackages is not inheritable. This means, that each of the tests, that wants to use the testers (basically 99%) will have to define that annotation in a repetitive manner.

Therefore the request is that this annotation should be marked as @Inherited for better DX.