Check for easy-to-handle cases of block param

[XrXr]

In some cases, methods taking block parameters don't require extra
paramter setup. They are fairly popular in railsbench.

[maximecb]

accepts_no_kwarg == false means the method accepts kwargs?

[XrXr]

Yea. For example, calling methods that only take position arguments with keywords is allowed:

def foo(a)
  p(a)
end

foo(key: 'word') # => {:key=>"word"}

We reject call kwarg call sites at the moment, though, just in case you are wondering how we deal with the kwargs to hash conversion.

The accepts_no_kwarg flag is for the **nil syntax:

def a(arg, **nil)
  p(arg)
end

a(key: 'word') # no keywords accepted (ArgumentError)

[maximecb]

Ok, I will merge this but I think this is the sort of thing that could be better commented, because it's really not obvious for people not intimately familiar with specific parts of CRuby.