Format doc comments on variant leafs smoother

[IwanKaramazow]

Fixes #2187
Improves readability of doc comments on variant leaves.

Before:

type myVariant =
  | /** super long doc comment forcing line break */
    A
  | /** second short doc comment */ B

After:

type myVariant =
  | /** super long doc comment forcing line break */
    A
  | /** second short doc comment */
    B;