Enforce trailing comma

[marcospgp]

Currently both including and not including the last comma in a list is allowed, such as:

            var mesh = new Mesh()
            {
                name = name,
                vertices = vs.ToArray(),
                triangles = ts.ToArray(),
                uv = uvs.ToArray(), // Comma here.
            };

            var mesh = new Mesh()
            {
                name = name,
                vertices = vs.ToArray(),
                triangles = ts.ToArray(),
                uv = uvs.ToArray() // No comma here.
            };

This should not be ambiguous, and in accordance with Prettier the trailing comma should be enforced.

[belav]

Duplicate of #668