Discriminated union decoding doesn't work with whitespace

[kubukoz]

Given this schema:

@discriminated("type")
union TestUnion {
  one: String,
  two: Integer
}

@discriminated("tpe")
union TestBiggerUnion {
  one: One,
  two: Two
}

structure One {
  value: String
}

structure Two {
  value: Integer
}

And this JSON:

""" { "tpe" : "one" , "value" : "hello" }"""

A failure is generated:

[error] [json] - Discriminated union decoding tolerates whitespace 46ms
[error] [json]   PayloadError: Expected JSON object, offset: 0x00000003, buf:
[error] [json]   +----------+-------------------------------------------------+------------------+
[error] [json]   |          |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f | 0123456789abcdef |
[error] [json]   +----------+-------------------------------------------------+------------------+
[error] [json]   | 00000000 | 20 7b 20 22 74 70 65 22 20 3a 20 22 6f 6e 65 22 |  { "tpe" : "one" |
[error] [json]   | 00000010 | 20 2c 20 22 76 61 6c 75 65 22 20 3a 20 22 68 65 |  , "value" : "he |
[error] [json]   | 00000020 | 6c 6c 6f 22 20 7d                               | llo" }           |
[error] [json]   +----------+-------------------------------------------------+------------------+

If all whitespace is removed from the JSON string, decoding succeeds.

Reproduction in #49.

[kubukoz]

As for the good news, dump-model produces a model that (after trimming whitespace between tokens) can be read by the default codecs :)