[Highlight Events] It is very unsual to conditionally use different interfaces but same event type for events

[smaug----]

HighlightPointerEvent extends PointerEvent and the explainer says:
"When a user performs a pointer action on part of an element containing a highlighted Range, a HighlightPointerEvent object must be fired"

In addition being odd unusual API behavior, it would make implementation of this all a bit harder than necessary.

[snianu]

@dandclark FYI