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/nested_dictionary.out

@@ -1,5 +1,5 @@
 GDTEST_OK
-{8:{"key":"value"}}
-{"key":"value"}
+{ 8: { "key": "value" } }
+{ "key": "value" }
 value
 value