[touch-events] TouchEvent should have a constructor (#10)

Most other event types have constructors defined these days.  TouchEvent should as well.  initTouchEvent was never standardized (though supported by some browsers), I suggest we go straight to standardizing a TouchEvent constructor (and I guess constructors for 'Touch' objects).

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/touch-events/issues/10