Fix a false positive for Lint/InheritException

[koic]

Fixes standardrb/standard#388 and reverts #3427.

This PR prevents the following false positive and auto-correction.

 class TestClass
-  FatalError = Class.new(Interrupt)
+  FatalError = Class.new(RuntimeError)
 end

Below is an inheritance tree for the exception classes.

        ---------------
        | BasicObject |
        ---------------
               ^
               |
        ---------------
        |   Kernel    |
        ---------------
               ^
               |
        ---------------
        |   Object    |
        ---------------
               ^
               |
        ---------------
        |  Exception  |
        ---------------
               ^
               |
      |------------------|
---------------  -----------------
|StandardError|  |SignalException|
---------------  -----------------
      ^                  ^
      |                  |
---------------  -----------------
|RuntimeError |  |   Interrupt   |
---------------  -----------------

As the inheritance tree shows, Interrupt is not is_a? in either StandardError or RuntimeError.

RuntimeError.new.is_a?(StandardError) #=> true
Interrupt.new.is_a?(StandardError)    #=> false
Interrupt.new.is_a?(RuntimeError)     #=> false

This goes against The Liskov Substitution Principle. Interup should not be replaced with StandardError or its subclasses.
Also, according to The Open/Closed Principle, Interrup class should be open to inheritance.

The same is true for SystemStackError, NoMemoryError, SecurityError, NotImplementedError, LoadError, SyntaxError, ScriptError, SignalException, and SystemExit classes.

This PR allows for exception handling according to Object-oriented principles and Ruby exception handling mechanism.

---

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• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
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• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
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[bbatsov]

The same is true for SystemStackError, NoMemoryError, SecurityError, NotImplementedError, LoadError, SyntaxError, ScriptError, SignalException, and SystemExit classes.

I was the impression that those classes should not be extended by application code, as they are internal to Ruby, plus usually they can't be handled in a meaningful way. I think this was also the main point of the special check for them - if you end up using those most likely you're doing something wrong.

[koic]

I think this Lint/InheritException cop has the role of protecting users from accidentally extending Exception class where they should extend StandardError or RuntimeError classes. This difference between Exception, StandardError, and RuntimeError may be mistaken by new Ruby user. I've seen some misunderstandings, especially among programmers skill transfering from Java to Ruby. This is because Java extends Exception class when creating custom exceptions.

On the other hand, I agree that it is rare for these exception classes to be extended at user layer, but these exception classes (e.g. LoadError) may be intentionally extended. In other words, it's possible that user intended it, not a mistake. So I think it's better to register an offense only with Exception.

[bbatsov]

Fair enough, let's simplify this.