[ruby-core:97310] [Ruby master Feature#16665] Add an Array#except_index method

Issue #16665 has been reported by alex_golubenko (Alex Golubenko).

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Feature #16665: Add an Array#except_index method
https://bugs.ruby-lang.org/issues/16665

* Author: alex_golubenko (Alex Golubenko)
* Status: Open
* Priority: Normal
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The main idea is to implement a method that we can use to exclude elements from the array by their indices.

For example:

``` ruby
%w( a b c d e f).except_index(0, -1) 
=> ["b", "c", "d", "e"]

%w( a b c d e f g h ).except_index(0..1, 3, -2..-1)
=> ["c", "e", "f"]
```

I was meeting many questions on the StackOverflow about how to do such functionality also found many topics about it.
So I think it might a helpful addition.

I spent a few days finding the proper solution on Ruby that might be acceptable with integers and ranges(both positive and negative) and has good performance: 

```ruby
  def except_index(*indexes)
    indexes.each_with_object(dup) do |ind, obj|
      ind.is_a?(Range) ? ind.each { |i| obj[i] = false } : obj[ind] = false
    end.select(&:itself)
  end
```

As you can see it's have not the best readability so I think it's a good point to add a built-in method on C.



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