Text editing behavior in BiDi is different between LeftArrow and Ctrl+LeftArrow

The easiest way to describe the problem is to show this snippet from the vello_editor example:

KeyCode::ArrowLeft => {
    self.selection = if ctrl {
        self.selection.previous_word(&self.layout, shift)
    } else {
        self.selection.previous_visual(
            &self.layout,
            self.cursor_mode,
            shift,
        )
    };
}

By default, pressing an arrow key moves your cursor in the visual direction of your key. But if you're doing ctrl+arrow, now the editor switches to "left means upstream, right means downstream". Both behaviors are mostly fine on their own (though "left means upstream" is latin-centric), but they're inconsistent with each other.

This behavior doesn't match either Chrome or Firefox.

(Parley's behavior with Home and End is also different from both Chrome and Firefox, but there's less of an inconsistency there, and Home/End support in BiDi is bad in both Chrome and Firefox anyway.)

Start with examples/vello_editor/src/text.rs, especially lines 168-178, and trace the previous_visual and previous_word entry points used for LeftArrow and Ctrl+LeftArrow. Compare their BiDi behavior with Chrome and Firefox. Done means arrow-key and Ctrl+arrow-key movement follow a consistent visual-direction model in BiDi text.