Numeric poly variant support

[IwanKaramazow]

Extends the grammar of poly variants with integers.

let one = #1

switch numericPolyVar {
| #89 => ()
}

type permissions = [
  | #777
  | #644
]

[bobzhang]

some more test cases:

type t = [
  | #1 (string)
  | #2 (int, string)
]

Note this is not very useful but to be consistent && the backed treats them in a uniform way.