Fix lightbox bug where panning results in carousel swipe

[cathyxz]

Fixes: double tap to zoom has a weird animation where you can’t move the image around after you have zoomed in.

[aghassemi]

looks like all the gesture handles preventDefault now. Maybe Gestures.get( doesn't need to the /* opt_shouldNotPreventDefault */true anymore? then we can remove all the event.preventDefault();.

Only one to double check is onPointerDown which preventsDefaults conditionally. Not sure what happens if it does it in all cases.

Approving the PR and leavings this to your discretion.

[cathyxz]

The reason why it has to be like this is because we only want to preventDefault AFTER the gesture triggers, but not when an event triggers a pending gesture. /* opt_shouldNotPreventDefault */false results in preventing default being called on single taps, which is why it broke lightbox toggle.

This should have happened in #12930.

[cvializ]

I understand wanting to get the fix in, but I would feel better about approving this if there was a TODO issue comment added to switch from using the window.event global to using the actual event object passed to the appropriate event listener.

[cathyxz]

So it's not possible to get an actual event, because gesture recognizers are triggered on a very specific series of touch start, touch move, and touch end events. It would be misleading to trigger on any of them, and implementation-wise messy to trigger on a click. I'm going to add a comment about revisiting this after resolving #12881.