`path.gerPrevSibling()` in traverse

[coderaiser]

Would be great to o have ability to get siblings (prev, next) while traversing AST, just like in Babel. I want to write transformation:

  (func (param $a i32) (param $b i32)
    (get_local $a)
    (get_local $b)
    i32.add
  )
  (export "add" (func $add))

To:

  func (param $a i32) (param $b i32)
    (i32.add (get_local $a) (get_local $b))
  )
  (export "add" (func $add))

I'm working on 🐊Putout linter, and wast also supported.

The most obvious way to do it would be to traverse i32.add and two previos siblings, and put them inside of i32.add.