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_lua_style.out

@@ -1,2 +1,2 @@
 GDTEST_OK
-{"a":1, "b":2, "with spaces":3, "2":4}
+{ "a": 1, "b": 2, "with spaces": 3, "2": 4 }