Fix formatComment to keep stable reformating and add comments unit tests

[clementdessoude]

Fix #279

As discussed in #279, it is impossible to know what is inside a block comment, and how it could be reformatted. So, as Prettier in JS, let's keep the original comment and its indentation when the comment is not JavaDoc (see https://prettier.io/docs/en/rationale.html#comments)

[jhaber]

👍 thanks for the quick fix

[lppedd]

@clement26695 another suggestion. Take for example this method definition.

public Long create(final InlineObject7 /* BackupItem */ dto) {

Currently it gets formatted as

public Long create(final InlineObject7 /* BackupItem */dto) {

So the space before dto is removed.
It would be better, if possible, to keep it.

---

My barbaric temporary fix

if (lines.length === 1) {
  res.push(lines[0] + ' ');
} else {
  lines.forEach(line => {
    res.push(line);
    res.push(prettier.literalline);
  });

  res.pop();
}

[Shaolans]

Is this what we want ?

[clementdessoude]

I will keep it in mind @lppedd ! I prefer to merge this as it is better than that we have right now but will try to find time to improve this