Add better `inspect` output for ExampleGroup

Pull Request for #1590 

The only problem I ran into was that the syntax error in the after hook test produces error output while running the spec (the test still passes).

> An error occurred in an `after(:context)` hook.
>   NoMethodError: undefined method `expcts' for #<RSpec::ExampleGroups::SomeClass_3 after(:context) hook>

This is definitely not ideal because it could distract from problems with "real" after hooks. The only two options I could up with were: 1) remove the test, or 2) add a way to suppress that error. I'm interested in your thoughts on the best way to handle this.
I had some trouble coming up with a spec to show that `@__inspect_output` was not included in `before_context_ivars`.

My thought process for the above was that if `@__inspect_output` were included in `before_context_ivars` then the `@__inspect_output` of `before(:context)` would be used for the `example`'s `@__inspect_output`.

I originally had an expectation of `expect(inspect_output).to_not eq("before(:context) hook")`, but changed it to the above since it was a stronger expectation. Maybe I should change it back to the negative check since it is clearer what I am testing? Or can you think of a better way to test this?