Add extract_idents pattern for :program tag

I wrote following code.

```ruby
def Assertion(&blk)
  ::PowerAssert.start(blk, assertion_method: __method__) do |tp|
    tp.yield
    puts tp.message_proc.call
  end
end

Assertion { "0".classs }
```

but outputs is only
```
Assertion { "0".class }
```

In this way, if assertion method is defined like `Kernel#Array`, cannot extract idents.

I think that it is better to add extract pattern. isn't it?