Improve dictionary printing to avoid confusion with arrays

- Add leading and trailing spaces within dictionaries, as the `{}`
  characters are hard to distinguish from `[]` on some fonts.
  This is especially helpful with empty arrays and dictionaries.

modules/gdscript/tests/scripts/parser/features/dictionary.out

@@ -7,8 +7,8 @@ null
 false
 empty array
 zero Vector2i
-{22:{4:["nesting", "arrays"]}}
-{4:["nesting", "arrays"]}
+{ 22: { 4: ["nesting", "arrays"] } }
+{ 4: ["nesting", "arrays"] }
 ["nesting", "arrays"]
 nesting
 arrays