move unit test helpers from AsgTools into new package AsgTesting

Merged Nils Erik Krumnack requested to merge krumnack/athena:asg_testing into 21.2

This may not be the right thing to worry about and may end up to be somewhat controversial, but it has also been bugging me for a while: So far the AsgTools library links directly against the google-test libraries, meaning that even in production code any package depending on AsgTools (which are a lot) will pull in the unit test library as a dependency. Admittedly that is pretty lightweight, but as a dependency it is completely unnecessary for anything except unit tests.

So what I did was split the unit test helpers into a separate package AsgTesting, and move unit tests from AsgTools into AsgExampleTools, which already holds some of the AsgTools unit tests. And then I also fixed up all the packages I broke with that update. Or at least fixed everything up for AnalysisBase, if there are any more dependencies in the other projects I wouldn't know.

cc @akraszna @ksuruliz

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