Hash#delete and Hash#clear don't check whether hash is frozen

[clayton-shopify]

> h = { 'a' => 1, 'b' => 2 }.freeze
 => {"a"=>1, "b"=>2}
> h.delete('a')
 => 1
> h
 => {"b"=>2}
> h.clear
 => {}

These operations should fail with can't modify frozen hash (RuntimeError).

This issue was reported by https://hackerone.com/an0n-j

[clayton-shopify]

The submitter suggested adding mrb_hash_modify calls to mrb_hash_delete and mrb_hash_clear.

[ksss]

I guess it need new method Kernel#frozen? to solve this issue.

E.g. Hash#delete_if

  def delete_if(&block)
    return to_enum :delete_if unless block_given?
+   raise RuntimeError, "can't modify frozen #{self.class}" if frozen?
    self.each do |k, v|
      self.delete(k) if block.call(k, v)
    end
    self
  end