OneCasePerLine rule doesn't format properly with existing line breaks

[ebgraham]

before formatting is appplied:

public enum TestEnum: Int {
  case a = 0,
    b = 1,
    c = 2
}

with OneCasePerLine formatting:

public enum TestEnum: Int {
  case a = 0
  case
    b = 1
  case
    c = 2
}

The correct format should be:

public enum TestEnum: Int {
  case a = 0
  case b = 1
  case c = 2
}

[allevato]

Presumably this is because we're keeping the leading newline trivia on the case's names. That's easy enough to remove.

It needs to be done with care though, since we'd also need to handle the following situations:

public enum TestEnum {
  case a,
    // line comment
    b,
    /* block comment */ c
}

The desired outcome for the line comment case is probably straightforward—move the trivia to the front of the injected case keyword:

  // line comment
  case b

For block comments, there's a bit more flexibility:

  /* block comment */ case c  ???
  case /* block comment */ c  ???

The first one is probably fine, and would at least be consistent with the line comment case.