Duplicate mouse events when acceptsFirstMouse: true

[oscarmarcelo]

Issue

When acceptsFirstMouse: true, if the clicked element also has attached events to the corresponding mouse event used to simulate the first click (See dispatch-first-click.js), it will end up triggering them twice, because the first click trick will also trigger them synthetically.

This is a specially unwanted behaviour when the said element is disabled (e.g. <button>), which shouldn't trigger click events.

Possible Fixes

The code used to run this should also check for the disabled state.
Also, it needs check if the element already has attached events to avoid making them run twice.

I would PR something for this, but honestly I haven't come up with a good solution to address the second part without affecting some obscure cases.
I can still send a PR and wait for someone help me, tough...

[mathieudutour]

We can maybe fix the first part and think about the second with a separate PR?