Support for `@foo.start` and `@foo.end`

[pokey]

Eg

(
  (aaa
    (bbb) @ddd.start
    (ccc) @ddd.end
  )
)

Creates @ddd node with range between @ddd.start and @ddd.end. If one of them is missing, just use the other one's range as the full range. Could also add exclusion args

Alternately, we could require that the user use a #make-range! operator

Eg

(
  (aaa
    (bbb) @ddd.start
    (ccc) @ddd.end
  )
  (#make-range! @ddd @ddd.start @ddd.end)
)

The advantage of this approach is that we could add exclusion args