[Fix #368] Add DelegateVisibilityMismatch cop

[Darhazer]

Flags delegate calls whose private: option does not match the surrounding visibility scope. delegate defines public methods by default and only supports a private: true option.

Replaces #1057
Handles the case of not explicit visibility set as suggested in #1057 (comment)
Closes #368

It includes auto-correct, marked unsafe, as it changes a method visibility.
I've tested on a large code private code base and found 2 cases when the delegated methods were actually used, even though they were under the private section in the class.

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• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
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• Added tests.
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