Ability to exclude analysis directories

[MichaelRFairhurst]

We should test that when analysis is disabled in the analysis_options.yaml that it also disables angular analysis. And likely we want the ability to turn off angular analysis for some directories even without having to turn off dart analysis for those directories.

This would be useful for, for instance, running the angular plugin on the angular codebase itself. If all tests which used invalidly configured components were in a separate directory than all tests that used valid setups, then they'd be able to get analysis errors in all their tests, but angular validation only where its supposed to be valid.