feature: @putout/plugin-remove-unreachable-code: backtracking parents and enhancements

[echo094]

If there are function declarations, other expressions can be deleted safely.

function fun2(f) {
  return 1;
  function m() {
  }
  return 2
}

As explained in #224, the next siblings in the parents can be deleted safely (except the function declarations):

let x3 = 1;
function fun3(f) {
  {
    let x3 = f + 2;
    return x3 * 2;
  }
  return 3;
}
fun3(x3)

[coderaiser]

Nice! Thank you!