Formatter removes judoc comment for aliases

[heueristik]

The formatter removes judoc comments for syntax aliases.

• Juvix v0.6.6-e4559bb

To Reproduce

1. Create a file with the following content and format it

import Stdlib.Prelude open;

--- The resource value type.
axiom Value : Type;

2. Replace the axiom with a syntax alias and format again.

- axiom Value : Type;
+ syntax alias Value := Nat;

3. observe the judoc comment being removed.

Expected behavior
The judoc comment should stay.

[lukaszcz]

It also happens for all other syntax declarations.