Split options for comma spacing for arrays versus objects

[Phrogz]

The before_comma, after_comma, around_comma options apply to both single-line arrays and objects.

• before_comma should become a shorthand for before_array_comma and before_object_comma.
• after_comma should become a shorthand for after_array_comma and after_object_comma.

We cannot have around_array_comma or around_object_comma because these would conflict and cause (even more) confusing inheritance. But that's OK; spacing around commas is not usually symmetric.