Added none flag to modifiers.rs

[ua-kxie]

allows pattern matching against no modifiers

match event {
    Event::Keyboard(iced::keyboard::Event::KeyPressed {
        key_code: iced::keyboard::KeyCode::C,
        modifiers: Modifiers::NONE,
    }) => {
        ...
    }
    Event::Keyboard(iced::keyboard::Event::KeyPressed {
        key_code: iced::keyboard::KeyCode::C,
        modifiers: Modifiers::CTRL,
    }) => {
        ...
    }
    ...
}

I haven't read into it much but it seems to me that the bitflags lib has some acknowledged shortcomings, which are addressed in some newer crates, e.g. flagset

#1868 may also be convenient to address in a modifiers rework

[ua-kxie]

so I was shown a way to match against no modifiers:

const NO_MODIFIER: Modifiers = Modifiers::empty();
match event {
    Event::Keyboard(iced::keyboard::Event::KeyPressed {
        key_code: iced::keyboard::KeyCode::C,
        modifiers: NO_MODIFIER,
    }) => {
        ...
    }
    Event::Keyboard(iced::keyboard::Event::KeyPressed {
        key_code: iced::keyboard::KeyCode::C,
        modifiers: Modifiers::CTRL,
    }) => {
        ...
    }
    ...
}

I will open a topic under discussions