Add option support for trailing comma in enums

[clementdessoude]

What changed with this PR:

• Add options support for trailing commas in enum and arrays

Example

options:

--trailing-comma all

// Input
public enum Enum {
  ONE, TWO, THREE
}

// Output
public enum Enum {
  ONE, 
  TWO,
  THREE,
}

// Input
public class T {
  void t() {
    int[] ints = { 1, 2, 3, };
    int[] ints = { aVeryLongArrayValue, anotherVeryLongArrayValue, andYetAnotherVeryLongArrayValue };
  }
}

// Output
public class T {
  void t() {
    int[] ints = { 1, 2, 3 };
    int[] ints = {
      aVeryLongArrayValue,
      anotherVeryLongArrayValue,
      andYetAnotherVeryLongArrayValue,
    };
  }
}

Relative issues or prs:
Relative to #313, #314 and #319

cc @natdempk and @jhaber

[murdos]

I'm not convinced that this is a feature we should support.
The prettier philosophy is to be opinionated and have few options, and I don't think a new option should be added here.

[clementdessoude]

I agree with you that options should be added very carefully, and this one could create a precedent. However, it is one of the very few options provided by Prettier, so we might consider it anyway

[murdos]

Ah, sorry! I was not aware that prettier already provided this option.
So definitely +1, we should indeed support it

[jhaber]

I believe array initializers are the only other part of the language that support trailing commas, we may want this option to apply there too:
https://docs.oracle.com/javase/specs/jls/se7/html/jls-10.html#jls-10.6

A trailing comma may appear after the last expression in an array initializer and is ignored.

For example: int[] ints = { 1, 2, 3, }

[clementdessoude]

Ok, so let's do this!

I added the trailing comma support in arrays too. I followed Prettier behavior which adds a comma (when the option is enabled) in arrays/objects only if they break