Unify pointer events and support tablet event - #3417

pub enum WindowEvent
    PointerMoved {
        device_id: Option<DeviceId>,
        position: PhysicalPosition<f64>,
        source: PointerSource,
    },
    PointerEntered {
        device_id: Option<DeviceId>,
        position: PhysicalPosition<f64>,
        primary: bool,
        kind: PointerKind,
    },
    PointerLeft {
        device_id: Option<DeviceId>,
        position: Option<PhysicalPosition<f64>>,
        primary: bool,
        kind: PointerKind,
    },
    PointerButton {
        device_id: Option<DeviceId>,
        state: ElementState,
        position: PhysicalPosition<f64>,
        primary: bool,
        button: ButtonSource,
        is_macos_activation_click: bool,
    },
}

pub enum WindowEvent {
    CursorMoved {
        device_id: DeviceId,
        position: PhysicalPosition<f64>,
    },
    CursorEntered { device_id: DeviceId },
    CursorLeft { device_id: DeviceId },
    MouseInput { device_id: DeviceId, state: ElementState, button: MouseButton },
    Touch(Touch),
}

pub enum Event {
    Mouse(mouse::Event),
    Touch(touch::Event),
}

pub enum Event {
    PointerEntered {
        position: Point,
        kind: pointer::Kind,
    },
    PointerLeft {
        kind: pointer::Kind,
    },
    PointerMoved {
        position: Point,
        source: pointer::Source,
    },
    PointerPressed {
        position: Point.
        button: button::Source,
    },
    PointerReleased {
        position: Point,
        button: button::Source,
    },
    WheelScrolled {
        delta: mouse::ScrollDelta,
    },
}

    pub fn is_primary_click(&self) -> bool { ... }
    pub fn is_primary_release(&self) -> bool { ... }
    pub fn is_secondary_click(&self) -> bool { ... }
    pub fn is_secondary_release(&self) -> bool { ... }

iced_core::Event::Mouse(mouse::Button::Left) | iced_core::Event::Touch(_) => { ... }

iced_core::Event::Pointer(event) if event.is_primary_click => { ... }