This change exludes internal and nested types from being treated as
controllers. This is consistent with MVC5's behavior.
DefaultActionSelectionConventions was primarily tested through running
action selection. I wanted to also test the methods with substantial logic
in this class, so I moved a spate of a classes from private classes inside of the
integration tests to public classes so they could be shared. I also added
tests to fill gaps in DefaultActionSelectionConventions, which is the vast
vast majority of this change.
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