The drawing logic follows the calculation logic in `Button::get_minimum_size`.
According to the order of `stylebox`, `icon`, and `text`, and follow properties
such as alignment mode, to fill the display space of the button.
Add a `Button::_set_h_separation_is_valid_when_no_text` for Button derived
classes (like `OptionButton`) that expects a `h_separation` between `icon`
and theme icon even if the `text` is empty.
f29a7d302e