to show unused block warning strictly.

```ruby
class C
  def f = nil
end

class D
  def f = yield
end

[C.new, D.new].each{|obj| obj.f{}}
```

In this case, `D#f` accepts a block. However `C#f` doesn't
accept a block. There are some cases passing a block with
`obj.f{}` where `obj` is `C` or `D`. To avoid warnings on
such cases, "unused block warning" will be warned only if
there is not same name which accepts a block.
On the above example, `C.new.f{}` doesn't show any warnings
because there is a same name `D#f` which accepts a block.

We call this default behavior as "relax mode".

`strict_unused_block` new warning category changes from
"relax mode" to "strict mode", we don't check same name
methods and `C.new.f{}` will be warned.

[Feature #15554]