Formatting empty dictionary deletes any comments and inserts invalid trailing comma

[mediremi]

This issue is present since v12.0.0-alpha.3.

The formatter strips comments from dictionaries without keys and inserts a syntactically invalid trailing comma:

// Before formatter

let _: dict<()> = dict{
  // a comment
}

// After formatter

let _: dict<unit> = dict{
  ,
}

Playground link