Pinch Gesture on web platform

Connected to: bevyengine/bevy#23421 # Description I am trying to detect pinch to zoom gestures when using `winit` on the web. This is problematic because pinch to zoom gestures use the same `MouseWheel` event scrolling uses. The only difference is that `event.ctrlKey` is set. This results in a hacky solution to try to detect whether the control key is pressed by listening to two separate events. ## Solution ~~Adding modifier state directly to the `MouseWheel` event and other events similar to it would allow higher ease of use for situations such as this one. Another solution could be to expose just a variable called `is_pinching` that represents the control key.~~ A new proposed solution is to send a pinch event when the `ctrlKey` modifier is sent during the event. ## Example JS Code ```javascript // current document.addEventListener('wheel', (e) => { dispatchModifiers(...) dispatchWheelEvent({ x: e.deltaX, y: e.deltaY }); }); // proposed document.addEventListener('wheel', (e) => { dispatchModifiers(...) if (!e.ctrlKey) dispatchWheelEvent({ x: e.deltaX, y: e.deltaY, modifiers: ... }); else dispatchPinchEvent({ … }); }); ```