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_mixed_syntax.out

@@ -1,2 +1,2 @@
 GDTEST_OK
-{"hello":{"world":{"is":"beautiful"}}}
+{ "hello": { "world": { "is": "beautiful" } } }