Pointer event support

[empyrical]

Introduction

I believe that W3C Pointer Events would be a perfect fit for inclusion in React Native in the future.

This discussion could serve as brainstorming for what various APIs/restrictions could be in place if these were implemented, or if this should be done at all.

The Core of It

They enable handling these kinds of inputs from the same event:

• touch - Already supported by current (and upcoming) RN APIs, but allows for code that handles all 3 types.
• mouse - Useful for desktop platforms, Android, and RNDom/RNWeb. Includes info on which button was pressed.
• pen - Could handle the Apple Pencil on iOS, Galaxy Note stylus (and others) on Android, Wacom, Surface Pen (and others) on desktop platforms. Includes pressure and tilt info.

The additional event props added would be:

• onPointerOver
• onPointerEnter
• onPointerDown
• onPointerMove
• onPointerUp
• onPointerCancel
• onPointerOut
• onPointerLeave
• onGotPointerCapture
• onLostPointerCapture

Of the bits of Fabric that are currently open sourced, there's a great W3C touch events implementation in the works:

https://github.com/facebook/react-native/blob/188cbb04ad264aea32ae235b85b61e626b767b83/ReactCommon/fabric/components/view/TouchEventEmitter.cpp

I suspect that a lot of this could be built on top of the work done on that. When Fabric is released, it'll be easier to reason about this.

Discussion points

• Should there be new components for pointer events in the vein of <TouchableWithFeedback />, like: <PointerPressWithFeedback />, <PointerOverWithFeedback />, etc?
• Being able to handle touch events in the Touch Events implementation and in Pointer Events might be seen as redundant. Is this an issue? If so, is there a better way to support desktop events in core react native? (Level 2 of Touch events will support Styluses too, so an additional area where it could be redundant)