New cop to narrow down assert_raises bodies

[fatkodima]

# bad
assert_raises(...) do
  some_other_code
  do_something
end

# good
some_other_code

assert_raises(...) do
  do_something
end

It is a good practice to make assert_raises bodies as small as possible, so that:

1. it is obvious which method call is tested for error
2. and when multiple calls inside assert_raises can raise the same kind of an exception, there won't be false positives and the right method is tested

So this cop will suggest that assert_raises body contains only 1 top level node and it should of send/csend type.

@koic Wdyt on this?

[koic]

This looks good to me. I think this cop can accept blocks (block type) as follows.

# good
assert_raises(...) do
  do_something do
    foo
    bar
  end
end