Suggest adding an event for `PointerInputDeviceChanges`

[mattrq]

An event to detect the capabilities of a pointer device have changed when the user switches between devices. Consider a Touchscreen laptop with pen support, a mouse and a trackpad; A user may switch between these frequently. Naming could be 'onPointerDeviceChangeoronPointerChange`.

Currently, to detect the capabilities of a device the code needs to listen to one of two types of pointer-events:

• One that fires frequently, e.g.pointerMove. Too frequent, requires additional overhead to ignore repeated calls for the same input type.
• One that fires at the point of interaction, e.g. 'pointerdown`. May be detected too late to switch input affordance changes.

It is unclear if events such as pointerover or pointerenter will refire if a user were to switch between mouse, trackpad or touch.