defect: Candid formatting is dodgy

[crusso]

• no space before :
• service types in arguments are formatted strangely

see test/mo-idl/ok/named.did.ok

service : {
  /// anon
  anon: (nat, nat) -> (nat); // no space before `:`
  /// escape candid keywords
  escape: ("int": int, "bool": bool, "service": service {  // <- weird break                                                                                
                                                }) -> ("int": int, "bool":
   bool, "service": service { // <- weird break
                    });
  /// function arg/ret
  f: (named: func (x: nat, y: nat) -> (r: nat)) -> (unamed:  // <- weird break
   func (nat, nat) -> (nat));
  /// actor arg/ret
  g: (A:
   service {
     anon: (nat, nat) -> (nat);
     named: (x: nat, y: nat) -> (r: nat);
   }) ->
   (service {
      anon: (x: nat, y: nat) -> (r: nat);
      named: (nat, nat) -> (nat);
    });
  /// named
  named: (x: nat, y: nat) -> (r: nat);
  /// record
  "record": (record {
               x: nat;
               y: nat;
             }) -> (record {r: nat;});
}